As Level Computer Science Book -1

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1.1 Information representation
1.1.1 Number Representation
Fundamentals of Data Representation:
Before we jump into the world of number systems, we'll need a point of reference; I recommend that you copy
the following table that you can refer to throughout this chapter to check your answers.
Hexadecimal Binary Denary
0 0000 0
1 0001 1
2 0010 2
3 0011 3
4 0100 4
5 0101 5
6 0110 6
7 0111 7
8 1000 8
9 1001 9
A 1010 10
B 1011 11
C 1100 12
D 1101 13
E 1110 14
F 1111 15
Denary/Decimal

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Denary is the number system that you have most probably grown up with. It is also another way of saying
base 10. This means that there are 10 different numbers that you can use for each digit, namely:
0,1,2,3,4,5,6,7,8,9
Notice that if we wish to say 'ten', we use two of the numbers from the above digits, 1 and 0.
Thousands Hundreds Tens Units
10^3 10^2 10^1 10^0
1000 100 10 1
5 9 7 3
Using the above table we can see that each column has a different value assigned to it. And if we know the
column values we can know the number, this will be very useful when we start looking at other base systems.
Obviously, the number above is: five-thousands, nine-hundreds, seven-tens and three-units.
5*1000 + 9*100 + 7*10 + 3*1 = (5973)10

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Binary Number System:
Binary is a base-2 number system, this means that there are two numbers that you can write for each digit 0, 1.
With these two numbers we should be able to write (or make an approximation) of all the numbers that we
could write in denary. Because of their digital nature, a computer's electronics can easily manipulate numbers
stored in binary by treating 1 as "on" and 0 as "off."
2^7 2^6 2^5 2^4 2^3 2^2 2^1 2^0
128 64 32 16 8 4 2 1
0 1 1 0 1 0 1 0
Using the above table we can see that each column has a value assigned to it that is the power of two (the base
number!), and if we take those values and the corresponding digits we can work out the value of the number:
1*64 + 1*32 + 1*8 + 1*2 = 106.
If you are asked to work out the value of a binary number, the best place to start is by labeling each column
with its corresponding value and adding together all the columns that hold a 1. Let's take a look at another
example:
(00011111)2
128 64 32 16 8 4 2 1
0 0 0 1 1 1 1 1
So now all we need to do is to add the columns containing 1s together:
1*16 + 1*8 + 1*4 + 1*2 + 1*1 = 31
Exercise: Binary
Convert the following binary numbers into denary
>>(00001100)2
Answer :
128 64 32 16 8 4 2 1
0 0 0 0 1 1 0 0
8+4 = (12)10
(01011001)2
Answer :
128 64 32 16 8 4 2 1
0 1 0 1 1 0 0 1
64 + 16 + 8 + 1 = (89)10
>>(00000111)2

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Answer :
128 64 32 16 8 4 2 1
0 0 0 0 0 1 1 1
4 + 2 + 1 = (7)10
>>(01010101)2
Answer :
128 64 32 16 8 4 2 1
0 1 0 1 0 1 0 1
64 + 16 + 4 + 1 = (85)10
How do we tell if a binary number is odd?
Answer :
It's right most digit is a one
Is there a short cut to working out a binary number that is made of solid ones, such as:
(01111111)2?
Answer :
Yes, take the first 0's column value and minus one
128 64 32 16 8 4 2 1
0 1 1 1 1 1 1 1
= 128 - 1 = 127 = 64 + 32 + 16 + 8 + 4 + 2 + 1

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Bit patterns in a computer:
The language that a computer understands is very simple, so simple that it only has 2 different numbers: 1 and
0. This is called Binary. Everything you see on a computer, images, sounds, games, text, videos, spreadsheets,
websites etc. Whatever it is, it will be stored as a string of ones and zeroes.
What is a bit?
A bit is the smallest unit in digital representation of information. A bit has only two values, ON and OFF
where ON is represented by 1 and OFF by 0. In terms of electrical signals a 1 (ON) is normally a 5 volt signal
and a 0 (OFF) is a 0 volt signal.
Bit
1
What is a nibble?
A group of 4 bits are referred to as a nibble.
Nibble
1 0 0 1
What is a byte?
In the world of computers and microcontrollers, 8 bits are considered to be a standard group. It is called
a byte. Microcontrollers are normally byte oriented and data and instructions normally use bytes. A Byte can
be broken down into two nibbles.
Byte
1 0 0 1 0 1 1 1
What is a word?
Going bigger, a group of bytes is known as a word. A word normally consists of two and sometimes more
bytes belonging together.
Word
1 1 0 1 0 1 1 0 0 0 1 1 0 1 1 1
Hexadecimal
You may notice from the table that one hexadecimal digit can represent exactly 4 binary bits. Hexadecimal is
useful to us as a shorthand way of writing binary, and makes it easier to work with long binary numbers.
Hexadecimal is a base-16 number system which means we will have 16 different numbers to represent our
digits. The only problem being that we run out of numbers after 9, and knowing that 10 is counted as two
digits we need to use letters instead:
0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F
We can do exactly the same thing as we did for denary and binary, and write out our table.

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16^5 16^4 16^3 16^2 16^1 16^0
1 048 576 65536 4096 256 16 1
0 0 3 4 A F
So now all we need to do is to add the columns containing values together, but remember that A = 10, B = 11,
C = 12, D = 13, E = 14, F = 15.
3*4096 + 4*256 + (A)10*16 + (F)15*1 = (13487)16
You might be wondering why we would want to use hexadecimal when we have binary and denary, and when
computer store and calculate everything in binary. The answer is that it is entirely for human ease. Consider
the
following example:
Error messages are written using hex to make it easier for us to remember and record them

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Representation Base
EFFE11 base-16 hexadecimal
15728145 base-10 denary
111011111111111000010001 base-2 binary
All the numbers are the same and the easiest version to remember/understand for humans is the base-16.
Hexadecimal is used in computers for representing numbers for human consumption, having uses for things
such as memory addresses and error codes. NOTE: Hexadecimal is used as it is shorthand for binary and
easier for people to remember. It DOES NOT take up less space in computer memory, only on paper or in
your head! Computers still have to store everything as binary whatever it appears as on the screen.

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Exercise: Hexadecimal
Convert the following Hex numbers into decimal/denary:
>>A1
Answer :
16 1
A 1
16 * 10 + 1 * 1 = (161)10
>>FF
Answer :
16 1
F F
16 * 15 + 1 * 15 = (255)10
>>0D
Answer :
16 1
0 D
16 * 0 + 1 * 13 = (13)10

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>> 37
Answer :
16 1
3 7
16 * 3 + 1 * 7 = (55)10
Why would we use the Hexadecimal system?
Answer :
Hexadecimal is used for humans, it is easier to understand and write
Name a use of the hexadecimal system?
Answer :
Hexadecimal is used for error message codes and memory addresses

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Converting Between Bases
The sum that you saw previously to convert from hex to denary seemed a little cumbersome and in the exam
you wouldn't want to make any errors, we therefore have to find an easier way to make the conversion.
Since 4 binary bits are represented by one hexadecimal digit, it is simple to convert between the two. You can
group binary bits into groups of 4, starting from the right, and adding extra 0's to the left if required, and then
convert each group to their hexadecimal equivalent. For example, the binary number 0110110011110101 can
be written like this:
0110 1100 1111 0101
and then by using the table given at the beginning, you can convert each group of 4 bits into hexadecimal:
0110 1100 1111 0101
(2+4=6) (4+8=12) (1+2+4+8=15) (1+4=5)
6 C F 5
So the binary number 0110110011110101 is 6CF5 in hexadecimal. We can check this by converting both to
denary. First we'll convert the binary number, since you already know how to do this:
32768 16384 8192 4096 2048 1024 512 256 128 64 32 16 8 4 2 1
0 1 1 0 1 1 0 0 1 1 1 1 0 1 0 1
32768*0 + 16384*1 + …….. 1*1 = 27893
By multiplying the columns and then adding the results, the answer is 27893.
Notice that the column headings are all 2 raised to a power, , , , , and so
on. To convert from hexadecimal to denary, we must use column headings that are powers with the base 16,
like this:
4096 256 16 1
6 C F 5

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(You should memorize the values A-F)
Totaling them all up gives us 27893, showing that 0110110011110101 is equal to 6CF5.
To convert from denary to hexadecimal, it is recommended to just convert the number to binary first, and then
use the simple method above to convert from binary to hexadecimal.
In summary, to convert from one number to another we can use the following rule:
Hexadecimal Binary  Denary

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Exercise: Hexadecimal and Base Conversion
Convert the following Hexadecimal values into Denary:
>>(12)16
Answer :
1 2 (Hex)
0001 0010 (Binary)
128 64 32 16 8 4 2 1
0 0 0 1 0 0 1 0
2+16 = 18 (decimal)
>> (A5)16
Answer :
A 5 (Hex)
1010 0101 (Binary)
128 64 32 16 8 4 2 1
1 0 1 0 0 1 0 1
128+32+4+1 = 165 (decimal)
>> (7F)16
Answer :
7 F (Hex)
0111 1111 (Binary)
128 64 32 16 8 4 2 1
0 1 1 1 1 1 1 1
64+32+8+4+2+1 = 127 (decimal)

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>> (10)16
Answer :
1 0 (Hex)
0001 0000 (Binary)
128 64 32 16 8 4 2 1
0 0 0 1 0 0 0 0
16(decimal)
Convert the following Binary numbers into hex:
>>(10101101)2
Answer :
1010 1101 (Binary)
A D (Hex)
Hence,(10101101)2 >> (AD)16
>>(110111)2
Answer :
0011 0111 (Binary)
3 7 (Hex)
Hence, (110111)2 >> (37)16
>>(10101111)2
Answer :
1010 1111 (Binary)
A F (Hex)
In this example, the question has
given you a binary number with only
six bits. You must complete the byte
by adding zeroes to the left of the
byte to make it complete

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>>(111010100001)2
Answer :
1110 1010 0001 (Binary)
E A 1 (Hex)
Hence, (111010100001)2 >> (EA1)16
Convert the following decimal numbers into hex:
>>(87)10
Answer :
128 64 32 16 8 4 2 1
0 1 0 1 0 1 1 1
0101 0111= 64+16+4+2+1 = 87(decimal)
0101 0111 (Binary)
5 7 (Hex)
Hence, (87)10>> (57)16
>>(12)10
Answer :
128 64 32 16 8 4 2 1
0 0 0 0 1 1 0 0
00001100 = 8+4 = 12(decimal)
0000 1100 (Binary)
0 C (Hex)
Hence, (12)10>> (0C)16

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>>(117)10
Answer :
128 64 32 16 8 4 2 1
0 1 1 1 0 1 0 1
01110101=64+32+16+4+1 = 117(decimal)
0111 0101 (Binary)
7 5 (Hex)
Hence, (117)10>> (75)16
Why might you use Hexadecimal?
Answer :
So that it makes things such as error messages and memory address easier for humans understand and
remember.
Give two uses of hexadecimal?
Answer :
Error message codes
Memory address locations

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Positive & negative Integers
Nearly all computers work purely in binary. That means that they only use ones and zeros, and there's no - or
+ symbol that the computer can use. The computer must represent negative numbers in a different way.
We can represent a negative number in binary by making the most significant bit (MSB) a sign bit, which will
tell us whether the number is positive or negative. The column headings for an 8 bit number will look like
this:
-128 64 32 16 8 4 2 1
MSB LSB
1 0 1 1 1 1 0 1
Here, the most significant bit is negative, and the other bits are positive. You start with -128, and add the other
bits as normal. The example above is -67 in denary because: (-128 + 32 + 16 + 8 + 4 + 1 = -67).
-1 in binary is: 11111111. (-128 + 127)
Note that you only use the most significant bit as a sign bit if the number is specified as signed. If the number
is unsigned, then the msb is positive regardless of whether it is a one or not.
Two’s Complement:
The MSB stays as a number, but is made negative. This means that the column headings are
-128 64 32 16 8 4 2 1
+117 does not need to use the MSB, so it stays as 01110101.
-117 = -128 + 11
= -128 + (8 + 2 + 1) fitting these in the columns give 10001011
Two’s complement seems to make everything more complicated for little reason at the moment, but later it
becomes essential for making the arithmetic easier.
The Standard ASCII Character Set

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Bytes are frequently used to hold individual characters in a text document. In the ASCII character set, each
binary value between 0 and 127 is given a specific character. Most computers extend the ASCII character set
to use the full range of 256 characters available in a byte. The upper 128 characters handle special things like
accented characters from common foreign languages.
You can see the 127 standard ASCII codes below. Computers store text documents, both on disk and in
memory, using these codes. For example, if you use Notepad in Windows OS to create a text file containing
the words, "Four score and seven years ago," Notepad would use 1 byte of memory per character (including 1
byte for each space character between the words --
ASCII character 32). When Notepad stores the sentence in a file on disk, the file will also contain 1 byte per
character and per space.
Try this experiment: Open up a new file in Notepad and insert the sentence, "Four score and seven years ago"
in it. Save the file to disk under the name getty.txt. Then use the explorer and look at the size of the file. You
will find that the file has a size of 30 bytes on disk: 1 byte for each character. If you add another word to the
end of the sentence and re-save it, the file size will jump to the appropriate number of bytes. Each character
consumes a byte.
If you were to look at the file as a computer looks at it, you would find that each byte contains not a letter but
a number -- the number is the ASCII code corresponding to the character (see below). So on disk, the numbers
for the file look like this:
Four and Seven (example)
F o u r <spc> a n d <spc> s e v e n
70 111 117 114 32 97 110 100 32 115 101 118 101 110
By looking in the ASCII table, you can see a one-to-one correspondence between each character and the
ASCII code used. Note the use of 32 for a space -- 32 is the ASCII code for a space. We could expand these
decimal numbers out to binary numbers (so 32 = 00100000) if we wanted to be technically correct -- that is
how the computer really deals with things.
The first 32 values (0 through 31) are codes for things like carriage return and line feed. The space character is
the 33rd value, followed by punctuation, digits, uppercase characters and lowercase characters. To see all 127
values try Google “ASCII codes”.

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UNICODE:
Unicode is a computing industry standard for the consistent encoding, representation and handling of text
expressed in most of the world's writing systems or languages. Developed in conjunction with the Universal
Character Set standard and published in book form as The Unicode Standard, the latest version of Unicode
consists of a repertoire of more than 107,000 characters covering 90 scripts for the correct display of text
containing both right-to-left scripts, such as Arabic and Hebrew, and left-to-right scripts).
The Unicode Consortium, the nonprofit organization that coordinates Unicode's development, has the
ambitious goal of eventually replacing existing character encoding schemes like ASCII with Unicode as many
of the existing schemes are limited in size and scope and are incompatible with multilingual environments.
Before 1996 UNICODE used 16 bits (2 bytes) however after 1996 size was not restricted to 16bits and
enhanced further to cover every possible variation of multilingual environment.
Notes: All the characters that a system can recognise are called its character set.
ASCII uses 8 bits so there are 256 different codes that can be used and hence 256 different characters. (This is
not quite true, we will see why in chapter 1.5 with reference to parity checks.)
A problem arises when the computer retrieves a piece of data from its memory. Imagine that the data is
01000001. Is this the number 65, or is it A?
They are both stored in the same way, so how can it tell the difference?
The answer is that characters and numbers are stored in different parts of the memory, so it knows which one
it is by knowing whereabouts it was stored.

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Binary Coded Decimal (BCD):
Some numbers are not proper numbers because they don’t behave like numbers. A barcode for chocolate
looks like a number, and a barcode for sponge cake look like a number, but if the barcodes are added together
the result is not the barcode for chocolate cake. The arithmetic does not give a sensible answer. Values like
this that look like numbers but do not behave like them are often stored in binary coded decimal (BCD). Each
digit is simply changed into a four bit binary number which are then placed after one another in order.
e.g. 398602 in BCD
Answer: 3 = 0011 9 = 1001
8 = 1000 6 = 0110
0 = 0000 2 = 0010
So 398602 = 001110011000011000000010 (in BCD)
Note: All the zeros are essential otherwise you can’t read it back.
Application
The BIOS in many personal computers stores the date and time in BCD because the MC6818 real-time clock
chip used in the original IBM PC AT motherboard provided the time encoded in BCD. This form is easily
converted into ASCII for display.
The Atari 8-bit family of computers used BCD to implement floating-point algorithms. The MOS
6502 processor used has a BCD mode that affects the addition and subtraction instructions.
Early models of the PlayStation 3 store the date and time in BCD. This led to a worldwide outage of the
console on 1 March 2010. The last two digits of the year stored as BCD were misinterpreted as 16 causing an
error in the unit's date, rendering most functions inoperable. This has been referred to as the Year 2010
Problem.

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1.1 Information
representation
1.1.2 Images
Graphic images that have been processed by a computer can usually be divided into two distinct categories.
Such images are either bitmap files or vector graphics. This section will cover the two main image types:
vector and bitmap, along with some compression techniques.
Bitmap Graphics
Bitmaps images are exactly what their name says they are: a collection of bits that form an image. The image
consists of a matrix of individual dots (or pixels) that all have their own color (described using bits, the
smallest possible units of information for a computer).
Let’s take a look at a typical bitmap image to demonstrate the principle:

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1.1 Information
representation
1.1.2 Images
Pixel
The smallest possible addressable area defined by a solid color, represented as binary, in an image
This example shows a Bitmap image with a portion greatly enlarged, in which the individual pixels are
rendered as little squares and can easily be seen. Try looking closely at your monitor or mobile phone screen
to see if you can spot the pixels
Resolution
Image Resolution - how many pixelsdoes an image contains per inch/cm? The more pixels used to produce
an image the more detailed that image can be i.e. the higher its resolution. For instance a 10 Megapixel digital
camera makes use of over 10 million pixels per image thus offering a very high photographic quality.
Screen Resolution - The screen resolution tells you how many pixels your screen can display horizontally
and vertically. It's written in the form 1024 x 768. In this example, the screen can show 1,024 pixels
horizontally, and 768 vertically:

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1.1 Information
representation
1.1.2 Images
The higher the resolution, the more pixels are available. Therefore the crisper the picture
There are many different video display formats out there, with different widths and heights, and total numbers
of pixels

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1.1 Information
representation
1.1.2 Images
Example: Calculating screen resolutions
Using the diagram above we are going to work out how many pixels are required to display a single frame on
a VGA screen.
Checking the resolution:
Height = 480
Width = 640
Area = Width x Height = Total Pixels
Area = 640 x 480 = 307200
Hence, it takes 307,200 pixels to display on a VGA screen!

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1.1 Information
representation
1.1.2 Images
Color depth - The number of bits used to represent the color of a single pixel
Colour
depth
1 bit 2 bit 4 bit
Example
Description Mono-chrome, only stores
black and white
stores 4 colours:
RGB(70,61,55),
RGB(79,146,85)
RGB(129,111,134),
RGB(149,146,166)
Stores limited colours
Number of
colors/pxl
Colour
depth
8 bit 24 bit
Example
Description close to reality hard to see any difference
between reality

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1.1 Information
representation
1.1.2 Images
It seems pretty obvious that the higher the color depth, the closer the picture will look to reality. Why then
don't we just ramp up the color depth on every image that we make? The answer should be obvious, for a
fixed resolution, the higher the resolution, the larger the file size.

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1.1 Information
representation
1.1.2 Images
Vector Graphics - images defined using mathematics and geometry such as points, lines, curves, and shapes
or polygon(s). Allowing for scalability. Objects and properties stored mathematically.
Drawing list - a set of commands used to define a vector image
Vector graphics are made up of objects and their properties. An object is a mathematical or geometrically
defined construct such as a rectangle, line or circle.
<rect ... />
<line ... />
<circle ... />

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1.1 Information
representation
1.1.2 Images
Each of these objects has properties to tell you the size, colour, position etc. Take a look at the next example
to see how drawing lists are built from objects and properties.
Rectangle Circle Combination
Image
Drawing
List
<rectx="14"y="23"
width="250"height="50
"
fill="green"
stroke="black"stroke-
width="1"/>
<circlecx="100"cy="100"r=
"50"
fill="red"
stroke="black"stroke-
width="5"/>
<rect
width="100"height="80"
x="0"y="70"
fill="green"/>
<line
x1="5"y1="5"
x2="250"y2="95"
stroke="red"/>
<circle
cx="90"cy="80"
r="50"
fill="blue"/>
<textx="180"y="60">
Un texte
</text>
Notes
x and y give the top left
start location
Note that the centre co-
ordinate is defined through
cx and cy
r gives the radius
Note that the circle is on top, this is
because it was drawn last.
To leave out an edge stroke don't put the
stroke command in.
The line has start x1,y1 and end x2,y2
coordinates.

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1.1 Information
representation
1.1.2 Images
Comparison between vector and bitmaps
This image illustrates the difference between bitmap and vector images. The bitmap image is composed of a
fixed set of dots (pixels), while the vector image is composed of a fixed set of shapes. In the picture, scaling
the bitmap reveals the pixels and scaling the vector image preserves the shapes.
Vector images scale without file size increase / decrease
Bitmap images scale resulting in file size increase / decrease
Vector images scale without distortion to the image
Bitmap images distort (pixelate) when scaling
Bitmaps are better for photo editing
Bitmaps require less processing power to display

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1.1 Information
representation
1.1.3 Sound
Sound is an oscillation of pressure transmitted through a solid, liquid, or gas (there is no sound in outer space
as space is a vacuum and there is no solid, liquid or gas to transmit sound through!). A speaker works by
moving its center cone in and out, this causes the air particles to bunch together forming waves. These waves
spread out from the speaker travelling at 340 m/s. If your ear is in the way, then the waves of sound particles
will collide with your ear drum, vibrating it and sending a message to your brain. This is how you hear:
When you hear different volumes and pitches of sound all that is happening is that each sound wave varies in
energy for the volume (larger energy waves, the louder the sound), or distance between sound waves which
adjusts the pitch, (smaller distances between waves leads to higher pitched sound).
1 - Base volume and frequency
2 - double volume and frequency
3 - same volume treble the frequency

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1.1 Information
representation
1.1.3 Sound
Sound is often recorded for two channels, stereo; feeding a left and right speaker whose outputs may differ
massively. Where one channel is used, this is called mono. 5.1 surround sound used in cinemas and home
media set ups use 6 channels.
A computer representation of a stereo song, if you look carefully you'll see the volume of the song varying as
you go through it
This section of the book will cover how we record, store and transmit sound using computers. Sound waves in
nature are continuous, this means they have an almost infinite amount of detail that you could store for even
the shortest sound. This makes them very difficult to record perfectly, as computers can only
store discrete data, data that has a limited number of data points.
Sound is a continuous set of data points
formed by a wave. Computers sample this
sound at discrete points to store a digital
approximation
The discrete approximations (in red) can be used to recreate
the original sound (grey). However, due to limitations in the
number of samples we take we are often unable to truly
represent a sound wave, though we can get close enough for
the human ear not to notice the difference.

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1.1 Information
representation
1.1.3 Sound
Analogue and digital
For a computer to store sound files we need to get the continuous analogue sound waves into discrete binary
values:
An analogue sound wave is picked up by a microphone and sent to an Analogue to Digital (ADC) converter in
the form of analogue electrical signals. The ADC converts the electrical signals into digital values which can
be stored on a computer.
Once in a digital format you can edit sounds with programs such as audacity.
To play digital audio you convert the sound from digital values into analogue electrical signals using the
DAC, these signals are then passed to a speaker that vibrating the speaker cone, moving the air to create sound
waves and analogue noise.
Analogue to Digital Converter (ADC) - Converts analogue sound into digital signals that can be stored on a
computer
Digital to Analogue Converter (DAC) - Converts digital signals stored on a computer into analogue sound
that can be played through devices such as speakers

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1.1 Information
representation
1.1.3 Sound
fig 1. The original analogue sound wave is a continuous set of points
fig 2. ADC converts sound into digital data
fig 3. DAC converts digital data into analogue sound, the analogue wave produced may differ significantly
from the original sound wave

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1.1 Information
representation
1.1.3 Sound
Sound Sampling
So we should know by now that sound waves are continuous and computers can only store discrete data. How
exactly does an Analogue to Digital Converter convert a continuous sound wave into discrete digital data? To
do this we need to look at how computers sample sound.
Sampling Rate - The number of samples taken per second
Hertz (Hz) - the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon
To create digital music that sounds close to the real thing you need to look at the analogue sound waves and
try to represent them digitally. This requires you to try to replicate the analogue (and continuous) waves as
discrete values. The first step in doing this is deciding how often you should sample the sound wave, if you do
it too little, the sample stored on a computer will sound very distant from the one being recorded. Sample too
often and sound stored will resemble that being recorded but having to store each of the samples means you'll
get very large file sizes. To decide how often you are going to sample the analogue signal is called the
sampling rate. Take a look at the following example:
Original Sound High sample rate
1/2 high sample
rate
1/3 high sample
rate
1/4 high sample
rate
original continuous
sound wave
digital looks like
original
digital loses
sharpness
loss of peaks
poor resemblance to
original!
To create digital sound as close to the real thing as possible you need to take as many samples per second as
you can. When recording MP3s you'll normally use a sampling rate between 32,000, 44,100 and 48,000Hz
(samples per second). That means that for a sampling rate of 44,100, sound waves will have been sampled
44,100 times per second! Recording the human voice requires a lower sampling rate, around 8,000Hz.
If you speak to someone on the phone it may sound perfectly acceptable, but try playing music down a
telephone wire and see how bad it sounds.

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1.1 Information
representation
1.1.3 Sound
Comparison of the same sound sample recorded at 8kHz, 22kHz and 44kHz sample rate. Note the spacing of
the data points for each sample. The higher the sample rate the more data points we'll need to store
Sampling resolution
Sampling resolution - the number of bits assigned to each sample
As you saw earlier, different sounds can have different volumes. The sampling resolution allows you to set the
range of volumes storable for each sample. If you have a low sampling resolution then the range of volumes
will be very limited, if you have a high sampling resolution then the file size may become unfeasible. The
sampling resolution for a CD is 16 bits used per sample.
File sizes
Bit rate - the number of bits required to store 1 second of sound
To work out the size of a sound sample requires the following equation:
File Size = Sample Rate * Sample Resolution * Length of sound
This is the same as saying:
File Size = Bit Rate * Length of sound
Let's look at an example:
Example: Sound File Sizes

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1.1.3 Sound
If you wanted to record a 30 second voice message on your mobile phone you would use the following:
Sample Rate = 8,000Hz
Sample Resolution = 16 bit
Length of Sound = 30 seconds
Therefore the total file size would be:
8,000 * 16 * 30 = 3 840 000 Bits = 480 000 Bytes
Sound Editing
If you are interested in sound editing you can start editing your own music using a program called Audacity.
Using Audacity you can create your own sound samples with different sample rates and sample resolutions,
listening to the difference between them and noting the different file sizes.
Features
This is a list of features in Audacity, the free, open source, cross-platform audio editor.
Recording
Audacity can record live audio through a microphone or mixer, or digitize recordings from cassette tapes,
records or minidiscs. With some sound cards, and on any Windows Vista, Windows 7 or Windows 8 machine,
Audacity can also capture streaming audio.
Import and Export
Import sound files, edit them, and combine them with other files or new recordings. Export your recordings in
many different file formats, including multiple files at once.
Sound Quality
Supports 16-bit, 24-bit and 32-bit (floating point) samples (the latter preserves samples in excess of
full scale).
Sample rates and formats are converted using high-quality resampling and dithering.
Tracks with different sample rates or formats are converted automatically in real time.
Editing
Easy editing with Cut, Copy, Paste and Delete.
Unlimited sequential Undo (and Redo) to go back any number of steps.
Edit and mix large numbers of tracks.
Multiple clips are allowed per track.

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1.1.3 Sound
Label tracks with selectable Sync-Lock Tracks feature for keeping tracks and labels synchronized.
Draw Tool to alter individual sample points.
Envelope Tool to fade the volume up or down smoothly.
Automatic Crash Recovery in the event of abnormal program termination.
Accessibility
Tracks and selections can be fully manipulated using the keyboard.
Large range of keyboard shortcuts.
Excellent support for JAWS, NVDA and other screen readers on Windows, and for VoiceOver on
Mac.
Effects
Change the pitch without altering the tempo (or vice-versa).
Remove static, hiss, hum or other constant background noises.
Alter frequencies with Equalization, Bass and Treble, High/Low Pass and Notch Filter effects.
Adjust volume with Compressor, Amplify, Normalize, Fade In/Fade Out and Adjustable Fade effects.
Remove Vocals from suitable stereo tracks.
Create voice-overs for podcasts or DJ sets using Auto Duck effect.
Other built-in effects include:
o Echo
o Paulstretch (extreme stretch)
o Phaser
o Reverb
o Reverse
o Truncate Silence
o Wahwah
Run "Chains" of effects on a project or multiple files in Batch Processing mode.
Plug-ins
Support for LADSPA, Nyquist, VST and Audio Unit effect plug-ins.
Effects written in the Nyquist programming language can be easily modified in a text editor - or you
can even write your own plug-in.
Analysis
Spectrogram view modes for visualizing frequencies.

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1.1.3 Sound
"Plot Spectrum" command for detailed frequency analysis.
"Sample Data Export" for exporting a file containing amplitude values for each sample in the
selection.
Contrast Analysis for analyzing average rms volume differences between foreground speech and
background music.
Support for adding VAMP analysis plug-ins.
Free and Cross-Platform
Licensed under the GNU General Public License (GPL).
Runs on Windows, Mac OS X and GNU/Linux

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1.1.4 Video
Video is an electronic medium for the recording, copying and broadcasting of moving visual images
characteristics of video streams.
Number of frames per second
Frame rate, the number of still pictures per unit of time of video, ranges from six or eight frames per second
(frame/s) for old mechanical cameras to 120 or more frames per second for new professional
cameras. PAL (Europe, Asia, Australia, etc.) and SECAM (France, Russia, parts of Africa etc.) standards
specify 25 frame/s, while NTSC (USA, Canada, Japan, etc.) specifies 29.97 frame/s. Film is shot at the slower
frame rate of 24 photograms/s, which complicates slightly the process of transferring a cinematic motion
picture to video. The minimum frame rate to achieve a comfortable illusion of a moving images about sixteen
frames per second.
Interlaced vs progressiveencoding
Video can be interlaced or progressive. Interlacing was invented as a way to reduce flicker in
early mechanical and CRT video displays without increasing the number of complete frames per second,
which would have required sacrificing image detail in order to remain within the limitations of a
narrow bandwidth. The horizontal scan lines of each complete frame are treated as if numbered consecutively
and captured as two fields: an odd field (upper field) consisting of the odd-numbered lines and an even
field (lower field) consisting of the even-numbered lines.
Analog display devices reproduce each frame in the same way, effectively doubling the frame rate as far as
perceptible overall flicker is concerned. When the image capture device acquires the fields one at a time,
rather than dividing up a complete frame after it is captured, the frame rate for motion is effectively doubled
as well, resulting in smoother, more lifelike reproduction (although with halved detail) of rapidly moving parts
of the image when viewed on an interlaced CRT display, but the display of such a signal on a progressive scan
device is problematic.
NTSC, PAL and SECAM are interlaced formats. Abbreviated video resolution specifications often include
an i to indicate interlacing. For example, PAL video format is often specified as 576i50, where 576indicates
the total number of horizontal scan lines, i indicates interlacing, and 50 indicates 50 fields (half-frames) per
second.
In progressive scan systems, each refresh period updates all of the scan lines of each frame in sequence. When
displaying a natively progressive broadcast or recorded signal, the result is optimum spatial resolution of both
the stationary and moving parts of the image. When displaying a natively interlaced signal, however, overall
spatial resolution will be degraded by simple line doubling and artifacts such as flickering or "comb" effects in
moving parts of the image will be seen unless special signal processing is applied to eliminate them. A
procedure known as deinterlacing can be used to optimize the display of an interlaced video signal from an
analog, DVD or satellite source on a progressive scan device such as an LCD Television, digital video
projector or plasma panel. Deinterlacing cannot, however, produce video quality that is equivalent to true
progressive scan source material.

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1.1.4 Video
Video compression method (digital only)
Video compression
Uncompressed video delivers maximum quality, but with a very high data rate. A variety of methods are used
to compress video streams, with the most effective ones using a Group Of Pictures (GOP) to reduce spatial
and temporal redundancy. Broadly speaking, spatial redundancy is reduced by registering differences between
parts of a single frame; this task is known as intraframe compression and is closely related to image
compression. Likewise, temporal redundancy can be reduced by registering differences between frames; this
task is known as interframe compression, including motion compensation and other techniques. The most
common modern standards are MPEG-2, used for DVD, Blu-ray and satellite television, and MPEG-4, used
for AVCHD, Mobile phones (3GP) and Internet.
Video formats
There are different layers of video transmission and storage, each with its own set of formats to choose from.
For transmission, there is a physical connector and signal protocol ("video connection standard" below). A
given physical link can carry certain "display standards" which specify a particular refresh rate, display
resolution, and color space.
Many analog and digital recording formats are in use, and digital video clips can also be stored on a computer
file system as files which have their own formats. In addition to the physical format used by the data storage
device or transmission medium, the stream of ones and zeros that is sent must be in a particular digital "video
encoding", of which a number are available.

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1.1.5 Compression techniques
Lossy and Lossless Compression
We have seen the various ways that you can reduce the size of files, we have also seen that humans have a
limit to the frequencies that they can perceive, so what sampling rate would be needed to only store the
samples that humans can perceive. The full range of human hearing is between 20 Hz and 20 kHz.
As you can see we have some serious issues with the size of sound files. Take a look at the size of a 3 minute
pop song recorded at a sample rate of 44kHz and a sample resolution of 16 bits.
44,000 * 16 * 180 = 126 720 000 bits (roughly 15 MB)
As you are probably aware an mp3 of the same length would be roughly 3Mb, a fifth of the size. So what
gives? It is easy to see that the raw file sizes for sounds are just too big to store and transmit easily, what is
needed it a way tocompress them.
Lossless
Lossless compression - compression doesn't lose any accuracy and can be decompressed into an identical
copy of the original audio data
WAV files don't involve any compression at all and will be the size of files that you have calculated already.
There are lossless compressed file formats out there such as FLAC which compress the WAV file into data
generally 50% the original size. To do this it uses run length encoding, which looks for repeated patterns in
the sound file, and instead of recording each pattern separately, it stores information on how many times the
pattern occurs in a row. Let us take a hypothetical set of sample points:
0000000000000000000001234543210000000000000000000123456787656789876
As you can see the silent area takes up a large part of the file, instead of recording these individually we can
set data to state how many silent samples there are in a row, massively reducing the file size:
(21-0)123454321(17-0)123456787656789876
Another technique used by FLAC files is Linear prediction.

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1.1.5 Compression techniques
Lossy
FLAC files are still very large, what is needed is a format that allows you to create much smaller file sizes that
can be easily stored on your computer and portable music device, and easily transmitted across the internet.
Lossy compression - compression loses file accuracy, generally smaller than lossless compression
As we have already seen, to make smaller audio files we can decrease the sampling rate and the sampling
resolution, but we have also seen the dreadful effect this can have on the final sound. There are other clever
methods of compressing sounds, these methods won't let us get the exact audio back that we started with, but
will be close. This is lossy compression.
There are many lossy compressed audio formats out there including: MP3, AAC and OGG (which is open
source). The compression works by reducing accuracy of certain parts of sound that are considered to be
beyond the auditory resolution ability of most people. This method is commonly referred to as perceptual
coding. It uses psychoacoustic models to discard or reduce precision of components less audible to human
hearing, and then records the remaining information in an efficient manner. Because the accuracy of certain
frequencies are lost you can often tell the difference between the original and the lossy versions, being able to
hear the loss of high and low pitch tones.
Example: Calculating file size for different colour depths
All the images above are of the same resolution:
300*225 = 67500 pixels
If the first image uses 1 bit to store the color for each pixel, then the image size would be:
Number of Pixels x Color Depth = Image Size
67500 * 1 bit = 67,500 bits
For the second image uses 2 bits to store the color for each pixel, then the image size would be:
Number of Pixels x Color Depth = Image Size
67500 * 2 bit = 135,000 bits

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Internet technologies
1.2.1 Networks
Introduction:
The history of computing started off with centralized computers (in many cases mainframes) or servers
performing all the calculations. Client computers were then attached to these centralised computers (servers)
and if you wanted to calculate something, you would have to wait for the central computer to respond. As
computing power got cheaper, client nodes became more powerful and the central computer less important.
However, with the growth of the internet, there has been a shift back to a client server model. Powerful central
computers store information such as emails, documents, music and videos or offer services such as file
hosting, printing, game hosting and internet access; client computers fetch information and use services from
these central servers. In the next few years you are likely to see more and more software moving away from
running on your desktop to running on remote servers and you accessing it as a client, this is called software
as a service.
The client-server model
As an example of modern client server model consider a video sharing website. The website, let's call it
mutube, has a server that stores all the videos that are uploaded to the site. The website is used by millions of
clients a day and each of them connects to the server to watch videos. When a client connects to mutube, the
server and asks for a particular video, the server loads the video into RAM from a large array of hard disks
and mutube sends the video to the client. The client on receiving the video presses play and watches the video.
Other examples of servers might be a shared printing service in a college. The print server will be hosted on a
single computer, and when anyone in the building wants to print, the request is sent to the server. In this case
the server will keep track of how much printing credit each user has and make sure that the print queue is dealt
with properly.
Extension: Cloud Computing
The current client-server model is starting to change, with companies being less likely to offer services with a
centralized server. Increasingly internet firms are reaching a global clientele, it makes little sense to have a
server or servers based in one location as if your servers are in America and some of your users in Armenia,
these users will experience slow access to your services. Another problem is if a power cut effects your server
or the connection to that one server or set of servers goes down then the service you are offering the internet
will also stop.

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With cloud computing the services may be distributed all over the globe, meaning that wherever you are,
you'll have a server reasonably close to you offering access to the data and services you need. It also means
that if one server goes down, other servers in different locations can keep the service running. Keeping
databases synchronized across the globe, so your mail client has the same mails in Switzerland as in
Swaziland, is a complex task and firms such as amazon and rackspace offer services to help you handle this.
One downside with cloud computing is you are never quite sure where your data is, and if you're not careful
you might find data being stored in countries that have less stringent data protection laws than your own.

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Server: a computer program running to serve the requests of other programs, the "clients"
Servers are software programs that in most cases run off normal computing hardware. Server software
includes:
Printing
File sharing
Game hosting
Websites
Other web services
Client: an application or system that accesses a service made available by a server
Clients are software programs and processes that connect to servers, sending requests and receiving responses.
Client examples include:
Web browser page requests
Chat systems on mobile phones
Online games
Definition: The term “WWW” refers to the “World Wide Web” or simply the Web. The World Wide Web
consists of all the public Web sites connected to the Internet worldwide, including the client devices (such as
computers and cell phones) that access Web content. The WWW is just one of many applications of the
Internet and computer networks.
The World Web is based on these technologies:
HTML - Hypertext Markup Language
HTTP - Hypertext Transfer Protocol
Web servers and Web browsers
Researcher Tim Berners-Lee led the development of the original World Wide Web in the late 1980s and early
1990s. He helped build prototypes of the above Web technologies and coined the term "WWW." Web sites
and Web browsing exploded in popularity during the mid-1990s.

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Internet
The Internet is named for "interconnection of computer networks". It is a massive hardware combination of
millions of personal, business, and governmental computers, all connected like roads and highways. The
Internet started in the 1960's under the original name "ARPAnet". ARPAnet was originally an experiment in
how the US military could maintain communications in case of a possible nuclear strike. With time, ARPAnet
became a civilian experiment, connecting university mainframe computers for academic purposes. As
personal computers became more mainstream in the 1980's and 1990's, the Internet grew exponentially as
more users plugged their computers into the massive network. Today, the Internet has grown into a public
spider web of millions of personal, government, and commercial computers, all connected by cables and by
wireless signals.
No single person owns the Internet. No single government has authority over its operations. Some technical
rules and hardware/software standards enforce how people plug into the Internet, but for the most part, the
Internet is a free and open broadcast medium of hardware networking.

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How internet works?
When you want to send a message or retrieve information from another computer, the TCP/IP protocols are
what make the transmission possible. Your request goes out over the network, hitting domain name servers
(DNS) along the way to find the target server. The DNS points the request in the right direction. Once the
target server receives the request, it can send a response back to your computer. The data might travel a
completely different path to get back to you. This flexible approach to data transfer is part of what makes the
Internet such a powerful tool.
Definition: A network gateway is an internetworking system capable of joining together two networks that
use different base protocols. A network gateway can be implemented completely in software, completely in
hardware, or as a combination of both. Depending on the types of protocols they support, network gateways
can operate at any level of the OSI model.
Because a network gateway, by definition, appears at the edge of a network, related capabilities
like firewalls tend to be integrated with it. On home networks, a broadband router typically serves as the
network gateway although ordinary computers can also be configured to perform equivalent functions.
Definition: Routers are small physical devices that join multiple networks together. Technically, a router is a
Layer 3 gateway device, meaning that it connects two or more networks and that the router operates at the
network layer of the OSI model.
Home networks typically use a wireless or wired Internet Protocol (IP) router, IP being the most common OSI
network layer protocol. An IP router such as a DSL or cable modem broadband router joins the home's local
area network (LAN) to the wide-area network (WAN) of the Internet.
By maintaining configuration information in a piece of storage called the routing table, wired or wireless
routers also have the ability to filter traffic, either incoming or outgoing, based on the IP addresses of senders
and receivers. Some routers allow a network administrator to update the routing table from a Web browser
interface. Broadband routers combine the functions of a router with those of a network switch and a firewall in
a single unit.

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Web Servers:
In general, all of the machines on the Internet can be categorized as two types: servers and clients. Those
machines that provide services (like Web servers or FTP servers) to other machines are servers. And the
machines that are used to connect to those services are clients. When you connect to Yahoo! at
www.yahoo.com to read a page, Yahoo! is providing a machine (probably a cluster of very large machines),
for use on the Internet, to service your request. Yahoo! is providing a server. Your machine, on the other hand,
is probably providing no services to anyone else on the Internet. Therefore, it is a user machine, also known as
a client. It is possible and common for a machine to be both a server and a client, but for our purposes here
you can think of most machines as one or the other.
A server machine may provide one or more services on the Internet. For example, a server machine might
have software running on it that allows it to act as a Web server, an e-mail server and an FTP server. Clients
that come to a server machine do so with a specific intent, so clients direct their requests to a specific software
server running on the overall server machine. For example, if you are running a Web browser on your
machine, it will most likely want to talk to the Web server on the server machine. Your Telnet application will
want to talk to the Telnet server, your e-mail application will talk to the e-mail server, and so on...
DNS:
It's like your computer's GPS for the
Internet. Its basic job is to turn a user-
friendly domain name like "google.com"
into an Internet Protocol (IP) address like
64.233.167.104 that computers use to
identify each other on the network.
Computers and other network devices on
the Internet use an IP address to route
your request to the site you're trying to
reach. This is similar to dialing a phone
number to connect to the person you're
trying to call. Thanks to DNS, though,
you don't have to keep your own address
book of IP addresses. Instead, you just
connect through a domain name server,
also called a DNS server or name server,
which manages a massive database that maps domain names to IP addresses.
Explain how communication systems are used to support the Internet: The Public Service Telephone
Network (PSTN), dedicated lines, cell phone network
PSTN (public switched telephone network) is the world's collection of interconnected voice-oriented public
telephone networks, both commercial and government-owned. It's also referred to as the Plain Old Telephone

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Service (POTS). It's the aggregation of circuit-switching telephone networks that has evolved from the days of
Alexander Graham Bell ("Doctor Watson, come here!"). Today, it is almost entirely digital in technology
except for the final link from the central (local) telephone office to the user.
In relation to the Internet, the PSTN actually furnishes much of the Internet's long-distance infrastructure.
Because Internet service providers ISPs pay the long-distance providers for access to their infrastructure and
share the circuits among many users through packet-switching, Internet users avoid having to pay usage tolls
to anyone other than their ISPs.
Many cell phone service providers offer mobile Broadband Internet Access Services for smartphones, basic
phones, tablets, netbooks, USB modems, mobile hotspots and other wireless devices over their 3G and 4G
broadband networks.
HSPA
HSPA (High Speed Packet Access) is a term used to describe certain 3G cellular network protocols. An
enhanced version of HSPA called HSPA+ or Evolved HSPA is also available on some carrier's networks.
Networking with Cell Phones and Cell Modems
Cell phones can be used as modems to connect computers to the Internet. Cellular cards (sometimes called
aircards) and routers also exist. Cell connections can be a convenient way to get online while traveling but are
typically slower than other forms of broadband Internet.
What Is Tethering?
Tethering is a method for configuring computers with wireless access to the Internet using a cell phone as a
modem. Tethering continues to grow in popularity but suffers from some important limitations compared to
other forms of broadband Internet access.

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GPRS
GPRS is an always-on packet switching service that supports theoretical data transfer rates up to 171 Kbps.
EV-DO - Evolution Data Only
EV-DO is a high-speed network protocol used for wireless Internet data communications.
HSDPA - High-Speed Downlink Packet Access
HSDPA is a network protocol for cellular telephone communications that supports theoretical maximum data
rates of 1.8 Mbps and higher. HSDPA is considered a third-generation (3G) mobile wireless technology.
LTE - Long Term Evolution
LTE is a wireless broadband technology designed to support mobile Internet access via cell phones and
handheld devices. LTE is sometimes referred to as a 4G (fourth generation) cellular standard as it offers
substantial improvements over older technologies.

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What are the benefits and drawbacks of using copper cable, fiber-optic cabling, radio waves,
microwaves, satellites?
Physical media; wires:
One of the key elements that determine bandwidth is the physical nature of the cable being used. A signal
becomes weaker and dies down eventually the longer it travels along a cable. Therefore the length of cable
determines the bandwidth of the link. For instance the bandwidth of a broadband DSL connection to the home
is determined by the length of copper cable between the house and the nearest telephone exchange.
Twisted pair cabling is a type of wiring in which two conductors (wires) are twisted together for the
purposes of cancelling out electromagnetic interference from external sources or other twisted pairs. It was
invented by Alexander Graham Bell. Twisted pair is used to gain enough bandwidth higher than coax cable.
Unshielded twisted pair (UTP) cable
Unshielded twisted pair or UTP cables are found in many local area networks and telephone systems. A
typical subset of these colours (white/blue, blue/white, white/orange, orange/white) shows up in most UTP
cables as shown above.
UTP cable is the most common cable used in computer networking and is often used in LAN because of its
relatively lower costs compared to optical fibre and coaxial cable. UTP is also finding increasing use in video
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Shielded twisted pair (STP) cables are often copper shielded in an attempt to prevent electromagnetic
interference and so allow bandwidth to be higher for any given length. This shielding can be applied to
individual pairs, to the collection of pairs or both.
Shielded twisted pair or STP
Copper cable is adequate for network cable runs for up to 100 meters, but above that the signal becomes too
weak, therefore an alternative technology is needed.
Fiber optics is a technology that uses glass (or plastic) threads (fibers) to transmit data. A fiber optic cable
consists of a bundle of glass threads, each of which is capable of transmitting messages modulated onto light
waves.
Fiber optic cable.

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Fiber optics has several advantages over traditional metal communications lines:
1. Fiber optic cables have a much greater bandwidth than metal cables. This means that they can carry
more data.
2. Fiber optic cables are less susceptible than metal cables to interference.
3. Fiber optic cables are much thinner and lighter than metal wires.
4. Data can be transmitted digitally (the natural form for computer data) rather than analogically.
The main disadvantage of fiber optics is that the cables are expensive to install. In addition, they are more
fragile than wire and are difficult to splice.
Fiber optics is a particularly popular technology for local-area networks. In addition, telephone companies are
steadily replacing traditional telephone lines with fiber optic cables. In the future, almost all communications
will employ fiber optics.
Wireless networks:
Wireless network refers to any type of computer network that is not connected by cables of any kind. It is a
method by which homes, telecommunications networks and enterprise (business) installations avoid the costly
process of introducing cables into a building, or as a connection between various equipment locations.
Wireless telecommunications networks are generally implemented and administered using a transmission
system called radio waves.

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Radio waves are an electromagnetic radiation with differing wavelengths. These waves are similar to an ocean
wave. Radio waves are used for many processes. For example they are used to broadcast TV, in
communication between satellites and it enables computers to share information without wires.
Radio waves have a large wavelength so they experience less interference and can travel over large distances.
However, since they do not have a high frequency, they cannot transmit as much data.
However, they can carry more signals than wires; they are often used for linking buildings on a college
campus or corporate site and increasingly for longer distances as telephone companies update their networks.
Microwave radio also carries computer network signals, generally as part of long-distance telephone systems.
Low-power microwave radio is becoming common for wireless networks within a building.
Microwave transmission refers to the technology of transmitting information by the use of electromagnetic
waves whose wavelengths are measured in centimeters; these are called microwaves. This part of the radio
spectrum ranges across frequencies of roughly 1.0 gigahertz (GHz) to 30 GHz. These correspond to
wavelengths from 30 centimeters down to 1 cm.
Microwaves are widely used for point-to-point communications because their small wavelength allows
conveniently-sized antennas to direct them in narrow beams, which can be pointed directly at the receiving
antenna. This allows nearby microwave equipment to use the same frequencies without interfering with each
other, as lower frequency radio waves do. Another advantage is that the high frequency of microwaves gives
the microwave band a very large information-carrying capacity; the microwave band has a bandwidth 30
times that of all the rest of the radio spectrum below it. The attenuation of microwave is less than twisted pair
or coaxial cable. A disadvantage is that microwaves are limited to line of sight propagation; they cannot pass
around hills or mountains as lower frequency radio waves can. It is also affected by anything blocking the line
of sight, such as rainfall.

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A satellite is any object that revolves around a planet in a circular or elliptical path. The moon is Earth's
natural satellite at 240,000 miles distant. Other satellites that fulfil this definition are man-made and have been
launched into orbit to carry out specific functions. These satellites are typically between 100 and 24,000 miles
away. Satellites have many purposes including data communications, scientific applications and weather
analysis. Satellite transmission requires an unobstructed line of sight. The line of site will be between the
orbiting satellite and a station on Earth. Satellite signals must travel in straight lines but do not have the
limitations of ground based wireless transmission, such as the curvature of the Earth.
Microwave signals from a satellite can be transmitted to any place on Earth which means that high quality
communications can be made available to remote areas of the world without requiring the massive investment
in ground-based equipment.

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What is a Bit Stream?
Millions of bits, travel over thousands of computer networks every day. The system works much like the
modern post office, which has to constantly send and receive letters from all over the world. Like those letters,
computer bits arrive in a continuous, ordered stream known as the bit stream. The bits identify where they are
coming from (often a computer) and where they are traveling to (often another computer).
All the information sent to and from a computer turns into a series of 1's and 0's that represent data. When the
computer sends a message, the bits travel in a specific order through a wire to their destination. Typically, the
bit stream starts with information about where it's going and how to process the information once it arrives.
An email, for example, contains information on the sender, the recipient, and the message itself. When the
user sends it, it's broken down into bits of data which travel over the bit stream to the recipient's computer.
Video on demand (VOD) is a system that may allow users to select and watch/listen to video or audio content
when they choose to, rather than having to watch at a specific broadcast time (Live streaming). Some TV
VOD systems such as Netflix or Hulu allow users to watch their favorite shows whenever they please.
Live streaming or real time, as the name suggests, is streaming a video that is happening at that exact
moment. Examples may be a football match, a concert, or a lecture happening at your university.

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What is Bitrate?
Bitrate is a term used to describe the amount of data that is being passed within a given amount of time.
Depending on the context, common measurements of bitrate include Kbps and Mbps, respectively meaning
kilobits per second and megabits per second. No matter the units being used, a higher number is generally
good, indicating high speed or high quality.
When it comes to Internet speeds, a higher bitrate is always desirable –it simply sends you the content that
you want faster. With higher bitrates, you can do more with your Internet connection — stream high-
definition movies, play online games with minimal lag, and download large files in just a few seconds. You
can figure out what bitrates you’re getting by visiting a website such as speedtest.net
When talking about streaming audio or video, bitrates refer to the amount of data stored for each second of
media that is played. For example, a 320 kbps MP3 audio file has a higher quality than the same file at just
128 kbps. The same applies to videos – a higher bitrate will have a higher quality when comparing the same
video with the same resolution. Bitrates should be expected to go up whenever the resolution goes up, as more
data is being processed. Therefore, high bitrates for audio and video may provide excellent quality, but it can
also place a major strain on your hardware which can result in stutters or frequent pauses in the media being
streamed if your bitrate is not high enough or if there is too much traffic on your line.

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1.2.2 IP addressing
An IP address (Internet Protocol Address) is an exclusive number that all IT devices (printers, routers,
modems, etc.) use which identifies and allows them the ability to communicate with each other on a computer
network.
Take for example, if you are ordering pizza by home delivery, then you need to tell the delivery man your
exact home address. Similarly, to print a document, you must know the IP address of your printer on your
network.
The designers of the Internet Protocol defined an IP address as a 32-bit number and this system, known
as Internet Protocol Version 4 (IPv4), is still in use today. However, due to the enormous growth of
the Internet and the depletion of vacant addresses, a new version of IP (IPv6), using 128 bits for the address,
was developed in 1995. IPv6 and its deployment has been ongoing since the mid-2000s.
IP addresses are binary numbers, but they are usually stored in text files and displayed in human-
readable notations, such as 172.16.254.1 (for IPv4), and 2001:db8:0:1234:0:567:8:1 (for IPv6).
In IPv4 an address consists of 32 bits which limits the
address space to 4,294,967,296 (232) possible unique
addresses. IPv4 reserves some addresses for special
purposes such as private networks (~18 million addresses)
IPv4 addresses are canonically represented in dot-decimal
notation, which consists of four decimal numbers, each ranging from 0 to 255, separated by dots,
e.g., 172.16.254.1. Each part represents a group of 8 bits (octet) of the address. In some cases of technical
writing, IPv4 addresses may be presented in various hexadecimal, octal, or binary representations.

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1.2.2 IP addressing
IP Address Formats
Originally IP addresses were divided into five classes as shown below. Classes A, B and C are the most
important: the initial bits determine which class an address belongs to, and the classes differ in how much of
the address is taken up with the network address and how much with the host address.

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1.2.2 IP addressing
What are Public IP Addresses?
A public IP address is assigned to every computer that connects to the Internet, where each IP is unique. In
this case, there cannot exist two computers with the same public IP address all over the Internet.
This addressing scheme makes it possible for the computers to “find each other” online and exchange
information. Users have no control over the IP address (public) that is assigned to the computer. The public IP
address is assigned to the computer by the Internet Service Provider as soon as the computer is connected to
the Internet gateway.
A public IP address can be either static or dynamic. A static public IP address does not change and is used
primarily for hosting web pages or services on the Internet. On the other hand, a dynamic public IP address is
chosen from a pool of available addresses and changes each time one connects to the Internet.
Most Internet users will only have a dynamic IP assigned to their computer which goes off when the computer
is disconnected from the Internet. Thus when it is re-connected it gets a new IP.
You can check your public IP address by visiting www.whatismyip.com
What are Private IP Addresses?
An IP address is considered private if the IP number falls within one of the IP address ranges reserved for
private networks such as a Local Area Network (LAN). The Internet Assigned Numbers Authority (IANA)
has reserved the following three blocks of the IP address space for private networks (local networks):
10.0.0.0 – 10.255.255.255 (Total Addresses: 16,777,216)
172.16.0.0 – 172.31.255.255 (Total Addresses: 1,048,576)
192.168.0.0 – 192.168.255.255 (Total Addresses: 65,536)
Private IP addresses are used for numbering the computers in a private network including home, school and
business LANs in airports and hotels which makes it possible for the computers in the network to
communicate with each other.
Say for example, if a network X consists of 10 computers, each of them can be given an IP starting
from 192.168.1.1 to 192.168.1.10. Unlike the public IP, the administrator of the private network is free to
assign an IP address of his own choice (provided the IP number falls in the private IP address range as
mentioned above).
Devices with private IP addresses cannot connect directly to the Internet. Likewise, computers outside the
local network cannot connect directly to a device with a private IP. It is possible to interconnect two private
networks with the help of a router.

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1.2.2 IP addressing
If the private network is connected to the Internet (through an Internet connection via ISP), then each
computer will have a private IP as well as a public IP. Private IP is used for communication within the
network whereas the public IP is used for communication over the Internet. Most Internet users with a DSL
connection will have both a private as well as a public IP.
You can know your private IP by typing ipconfig command in the command prompt. The number that you see
against “IPV4 Address:” is your private IP which in most cases will be192.168.1.1 or 192.168.1.2. Unlike the
public IP, private IP addresses are always static in nature.
Explain how a Uniform Resource Locator (URL) is used to locate a resource on the World Wide
Web (WWW) and the role of the Domain Name Service
Every file on the Web has a URL (uniform resource locator). Whether it’s an HTML file, a photo file,
whatever, it has a URL.
A file’s URL is its unique address on the Web. Just as a cell phone has a unique telephone number, a file has a
unique URL.
Suppose that a browser shows this:
It comes from this HTML.
<a href="http://doomdogs.com/products/ball.html">Bouncing ball</a>
There are two parts to the link. First, there’s the text shown to the user. That’s “Bouncing ball.” Second,
there’s a URL: http://doomdogs.com/products/ball.html. That’s where the browser will go if the link is
clicked.
Getting a page
A user clicks the “Bouncing ball” link. What does the browser do?
First, it creates an HTTP GET request. The request looks something like this:
GET /products/ball.html HTTP/1.1

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1.2.2 IP addressing
The message is sent to a server. Which server? The one given in the URL of course.
The URL of the desired page is http://doomdogs.com/products/ball.html. The first part “http” is the service-
layer communication protocol to use. The second part“doomdogs.com” is the domain name of the server. So
that’s where the message is sent: to the server at doomdogs.com.The rest of the URL “/products/ball.html”
tells the server what data to return to the browser. That part of the URL matches a file on the server. A server
might have 50,000 files that it can send to a browser. /products/ball.html is the particular file it should send.
Why is the user’s browser showing him a link? Because of this HTML:
“<a href="http://doomdogs.com/products/ball.html">Bouncing ball</a>”
This link says to show the text “Bouncing ball.” If Jake clicks on it, his Web browser will jump to the
page “http://doomdogs.com/products/ball.html.”
Let’s look at what happens when the user clicks the link.

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1.2.2 IP addressing
The user clicks on the link. The browser looks at the code that created the link. The code is:<a
href="http://doomdogs.com/products/ball.html">Bouncing ball</a>
So the browser knows it should show the page “http://doomdogs.com/products/ball.html” the browser creates
an HTTP message to doomdogs.com: GET /products/ball.html. The Internet sends the message to the Web
server.
The server at doomdogs.com is a computer, with a hard disk spinning away. It runs the UNIX operating
system. (Not which is to our concern)
If you looked on the server’s disk drive, you would see a file with the path/sites/dd/products/ball.html.
This is the file with information on the bouncing ball.
Somehow, we want the Web server to use the URL the browser sent, to fetch the right file from its disk drive.
It needs to convert the URL into a file path, then use the file path to read the file.
Suppose the server is running the Apache Web server software (it’s the most popular in the world). Apache
has a configuration file, created by the DoomDog’s Web master. The file tells Apache how to run.
One of the settings in the file is DocumentRoot. The setting tells Apache where on the computer’s disk drive
the files for the Web site are stored.

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1.2.2 IP addressing
The Web master puts all the data for the doomdogs.com Web site in the directory “/sites/dd”. Then he
set DocumentRoot to “/sites/dd”, so that Apache would know where to get the files.
The server takes its DocumentRoot setting “/sites/dd” and appends the URL path “/products/ball.html”,
giving “/sites/dd/products/ball.html.”
Now Apache knows where to get the file the browser
asked for. We’re at step 3. Apache has translated
the URL to a file path on the server computer’s disk drive.
Apache reads the file, and sends its contents back to the
browser. The browser renders the content for Jake (6). Recall that rendering is the process of making a display
from code in a file.
And finally the contents are displayed on the screen
What is a DNS server?
The Domain Name System (DNS) is a standard technology for managing public names of Web sites and other
Internet domains. DNS technology allows you to type names into your Web browser like “soundcloud.com”
and your computer to automatically find that address on the Internet. A key element of the DNS is a
worldwide collection of DNS servers.
A DNS server is any computer registered to join the Domain Name System. A DNS server runs special-
purpose networking software, features a public IP address, and contains a database of network names and
addresses for other Internet hosts.
A DNS server is similar to looking up contacts on your phone, to call a contact, you simply look up that
person’s name, but that name is of no use to the phone itself, it has to look up the contact number and dial
that.
Simply speaking, both systems translate the website/contact name into an IP address or phone number.

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1.2.2 IP addressing
DNS Root Servers
DNS servers communicate with each other using private network protocols. All DNS servers are organized in
a hierarchy. At the top level of the hierarchy, so-called “root servers” store a complete database of Internet
domain names and their corresponding IP addresses. The Internet employs 13 root servers that have become
somewhat famous for their special role. Maintained by various independent agencies, the servers are aptly
named A, B, C and so on up to M. Ten of these servers reside in the United States, one in Japan, one in
London, UK and one in Stockholm, Sweden.
How DNS Works
The DNS is a distributed system, meaning that only the 13 root servers contain the complete database of
names and addresses. All other DNS servers are installed at lower levels of the hierarchy and maintain only
certain pieces of the overall database.
Most lower level DNS servers are owned by businesses or Internet Service Providers (ISPs). For example,
Google maintains various DNS servers around the world that manage the google.com, google.co.uk, and other
domains. Your ISP also maintains DNS servers as part of your Internet connection setup.
DNS networking is based on the client / server architecture. Your Web browser functions as a DNS client
(also called DNS resolver) and issues requests to your Internet provider's DNS servers when navigating
between Web sites.
When a DNS server receives a request not in its database (such as a geographically distant or rarely visited
Web site), it temporarily transforms from a server to a DNS client. The server automatically passes that
request to another DNS server or up to the next higher level in the DNS hierarchy as needed. Eventually the
request arrives at a server that has the matching name and IP address in its database (all the way to the root
level if necessary), and the response flows back through the chain of DNS servers to your computer.
DNS and the World Wide Web
All public Web sites run on servers connected to the Internet with public IP addresses . The Web servers
at About.com, for example, have addresses like 207.241.148.80. Although people can type address
information like http://207.241.148.80/ into their Web browser to visit sites, being able to use proper names
like http://www.about.com/ is much more practical. The Internet utilizes DNS as a worldwide name resolution
service for public Web sites. When someone types a site's name into their browser, DNS looks up the
corresponding IP address for that site, the data required to make the desired network connections between
Web browsers and Web servers.

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1.2.3 Client- and server-side scripting
There are two main ways to customize Web pages and make them more interactive. The two are often used
together because they do very different things.
Scripts
A script is a set of instructions. For Web pages they are instructions either to the Web browser (client-side
scripting) or to the server (server-side scripting). These are explained more below.
Scripts provide change to a Web page. Think of some Web pages you have visited. Any page which changes
each time you visit it (or during a visit) probably uses scripting.
All log on systems, some menus, almost all photograph slideshows and many other pages use scripts. Google
uses scripts to fill in your search term for you, to place advertisements, to find the thing you are searching for
and so on. Amazon uses scripting to list products and record what you have bought.
Client-side
The client is the system on which the Web browser is running. JavaScript is the main client-side scripting
language for the Web. Client-side scripts are interpreted by the browser. The process with client-side scripting
is:
1. the user requests a Web page from the server
2. the server finds the page and sends it to the user
3. the page is displayed on the browser with any scripts running during or after display
So client-side scripting is used to make Web pages change after they arrive at the browser. It is useful for
making pages a bit more interesting and user-friendly. It can also provide useful gadgets such as calculators,
clocks etc. but on the whole is used for appearance and interaction.
Client-side scripts rely on the user's computer. If that computer is slow they may run slowly. They may not
run at all if the browser does not understand the scripting language. As they have to run on the user's system
the code which makes up the script is there in the HTML for the user to look at (and copy or change).

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Server-side
The server is where the Web page and other content lives. The server sends pages to the user/client on request.
The process is:
1. the user requests a Web page from the server
2. the script in the page is interpreted by the server creating or changing the page content to suit the user
and the occasion and/or passing data around
3. the page in its final form is sent to the user and then cannot be changed using server-side scripting
The use of HTML forms or clever links allow data to be sent to the server and processed. The results may
come back as a second Web page.
Server-side scripting tends to be used for allowing users to have individual accounts and providing data from
databases. It allows a level of privacy, personalization and provision of information that is very powerful. E-
commerce, MMORPGsand social networking sites all rely heavily on server-side scripting.
PHP and ASP.net are the two main technologies for server-side scripting.
The script is interpreted by the server meaning that it will always work the same way. Server-side scripts are
never seen by the user (so they can't copy your code). They run on the server and generate results which are
sent to the user. Running all these scripts puts a lot of load onto a server but none on the user's system.
The combination
A site such as Google, Amazon, Facebook or StumbleUpon will use both types of scripting:
server-side handles logging in, personal information and preferences and provides the specific data
which the user wants (and allows new data to be stored)
client-side makes the page interactive, displaying or sorting data in different ways if the user asks for
that by clicking on elements with event triggers

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To insert a JavaScript into an HTML page, we use the <script> tag,inside the <script> tag we use the
“type”attribute to define the scripting language.
JavaScript code and blocks
JavaScript code is a sequence of JavaScript statements.
Each statement is executed by the browser in the sequence they are written
JavaScript statements are grouped together in a block.
Blocks start with a left curly bracket and ends with a right curly bracket.
The purpose of blocks is to make the sequence of statements execute together.
JavaScript operators
Arithmetic operators
Assignment operators
Comparison operators
Logical operators
Conditional operator

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Alert Box:
An alert box is often used if you want to make sure information comes through to the user.
When an alert box pops up, the user will have to click “OK” to proceed.
Syntax: alert(“sometext”);
Confirm Box:
A confirm box is often used if you want the user to verify or accept something.
When a confirm box pops up, the user will have to click either “OK” or “cancel’ to proceed.
If the user clicks “OK”, the box returns true. If the user clicks “cancel”, the box returns false.
Syntax: confirm(“sometext”);
Prompt Box:
A prompt box is often used if you want the user to input a value before entering a page.
When a prompt box pops up, the user will have to click either “OK’ or “cancel” to proceed after
entering an input value.
If the user clicks “OK” the box returns the input value. If the user clicks “cancel” the box returns null.
Syntax:prompt (“sometext”, “defaultvalue”);
JavaScript functions
A function contains a code that will be executed by an event or by a call to the function.
We may call a function from anywhere within a page
Functions can be defined both in the <head> and in the <body> section of a document
Syntax :- Function function name(var1, var2…varx) {Some code}

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JavaScript events
Events are the beating heart of any JavaScript application.
This gives us an overview of what event handling is , what its problems are and how to write proper
cross-browser scripts
Without events there are no scripts.
Whenever a user of JavaScript takes action, he causes an event.
Event modeling
This is example of event modeling in which we displays the date when a button is clicked:

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Server side scripting as mentioned earlier is a web server technology in which a user’s request is fulfilled by
running a script directly on the web server to generate dynamic web pages. A common scripting language for
server scripting is “PHP”
Uses of PHP:
Performs system functions i.e. from files on a system it can create,open,read, write and close them.
Can handle forms, i.e. gather data from files, save data to file, through email you send data, and return
data to the user.
Add , delete or modify elements within your database through PHP
It can restrict users to access some pages of any website
It can encrypt data.
Basic Syntax for PHP:
The PHP parsing engine needs a way to differentiate PHP code from other elements in the page. The
mechanism for doing so is known as “escaping to PHP”.
We have canonical PHP tags.
The most universally effective PHP tag style is “<?php….?>”
Ways of sending information:
There are 2 ways of sending information to the web browser:
1. The GETMethod
2. The POST Method

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The GET method
Before the browser sends the information, it encodes it using a scheme called URL encoding.
In this scheme, name/value pairs are joined with equal signs and different pairs are separated by the
ampersand sign (&).
Spaces are removed and replaced with the “+” character and any other non-alphanumeric characters
are replaced with a hexadecimal values.
The get method sends the encoded user information appended to the page request.
The page and the encoded information are separated by the “?” character.
“http://www.test.com/index.htm?name1=value1&name2=value2”
The get method produces a long string that appears in your server logs, in the browser’s location “:
box”.
The GET method is restricted to send up to 1024 characters only
Never use GET method if you have a password or other sensitive information to be sent to the user.
It can’t be used to send binary data, like images or word documents, to the server.
The data sent by the GET method can be accessed using the QUERY_STRING environment variable.
The PHP provides $_GET associative array to access all the sent information using the GET method.

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Here is an example of simple PHP code using the GET method:
<?php
if( $_GET["name"] || $_GET["age"] )
{
echo "Welcome ". $_GET['name']. "<br />";
echo "You are ". $_GET['age']. " years old.";
exit();
}
?>
<html>
<body>
<form action="<?php $_PHP_SELF ?>" method="GET">
Name: <input type="text" name="name" />
Age: <input type="text" name="age" />
<input type="submit" />
</form>
</body>
</html>
The POST method:
The POST method transfers information via HTTP headers. The information is encoded as described in case
of GET method and put into a header called “QUERY_STRING”.
The POST method does not have any restriction on data size to be sent.
The POST method can be used to send ASCII as well as binary data.
The data sent by POST method goes through HTTP header so the security depends on the HTTP
protocol. By using Secure HTTP you can make sure that your information is secure.
The PHP provides “$_POST” associative array to access all the sent information using POST method.

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Here is an example of simple PHP code using the POST method:
<?php
if( $_POST["name"] || $_POST["age"] )
{
echo "Welcome ". $_POST['name']. "<br />";
echo "You are ". $_POST['age']. " years old.";
exit();
}
?>
<html>
<body>
<form action="<?php $_PHP_SELF ?>" method="POST">
Name: <input type="text" name="name" />
Age: <input type="text" name="age" />
<input type="submit" />
</form>
</body>
</html>
PHP variables
All variables in PHP are denoted with a leading dollar sign “$”.
The value of variable is the value of its most recent assignment.
PHP does a good job of automatically converting types from one to another when necessary.
Variables in PHP do not have intrinsic types.
(a variable does not know in advance whether it will be used to store a number or a string of
characters.)

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Data types in PHP
INTERGERS: are whole numbers, without a decimal point, like “574”.
DOUBLES: are floating point numbers, like “3.146”.
BOOLEANS: have only two possible values either “true” or “false”.
NULL: null is a special type that only has one value i.e. “null”.
STRINGS: are sequences of characters like “hello friends”
Arrays: arrays are names and indexed collection of other values.

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PHP control structures
if…..else statement :
Use this statement if you want to execute some code if a condition is true and another code if a condition is
false.
Example:
if (condition)
Code to be executed if condition is true;
else
Code to be executed if condition is false;
else if statement:
If you want to execute some code if one of the several conditions aretrue, use this statement.
Example:
if (condition)
Code to be executed if condition is true;
else if (condition)
Code to be executed if condition is true
Else
Code to be executed if condition is false;

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Switch statement:
If you want to select one of many blocks of code to be executed , use the switch statement.
Example:
switch(expression)
{
case label 1
Code to be executed if expression=label 1;
break;
case label 2
Code to be executed if expression= label 2;
break;
default:
code to be executedif expression is different from both label 1 and label
2;

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1.3 Hardware
1.3.1 Input, output and storage devices
Computer System:
A computer is an electronic machine that accepts data, stores and processes data into information. The
computer is able to work because there are instructions in its memory directing it, instructions that direct the
computer are called software or computer program. The physical parts of the computer that you can see and
touch, such as the keyboard, monitor and the mouse are called hardware. There are four major categories of
computer hardware:
1. Input devices: used to enter data into the computer
2. Processing devices: manipulate the data.
3. Storage devices: store data and program.
4. Output device: show results of the process.
Input devices:
An input device is any hardware component that allows you the user to enter data or instruction into the
computer. There are many manual/automatic input devices. Most widely used input devices are:
Keyboard
Pointing devices
o Trackerball mouse
o Laser mouse
2D/3D Scanners
Keyboard:

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1.3 Hardware
The keyboard is one of the most popular ways of inputting information into a computer. The basic mechanical
keyboard relies on springed keys being pressed down to complete an electrical circuit. This circuit then
transmits a binary signal (commonly using ASCII) to the computer to represent the key pressed.
Scanner
A scanner creates a digital photograph of a paper document. It scans the illuminated surface of the document
with a single row of hundreds of light sensors. Each sensor produces an analogue signal that depends on the
intensity of the light it receives. The scanner’s embedded computer repeatedly scans the signals from the
sensors as they move across the document. The embedded computer then digitizes, processes them and sends
them to the computer.

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1.3 Hardware
Fingerprint Scanner
The ridges and troughs on a person's finger and toes are unique to
that person. Using a scanner a finger print pattern can be recorded
and compared to others on a database, allowing a computer to
match finger prints from crimes to a suspect, or to allow people
into restricted areas.
Retina Scanner
Retina scanners are used to record the pattern of blood vessels at the back of
someone's eye. As every has a different pattern of vessels, then retina scanners
can be used to uniquely identify people and are very difficult to fake.
Iris Scanner:
By taking a picture of the blood vessels and colouring of someone's eye, we can
get a unique pattern that can be used to identify individuals. People might try and
circumvent this by using contact lenses
Trackerball Mouse:
A trackball is a pointing device consisting of a ball held by a socket containing sensors to detect a rotation of
the ball about two axes—like an upside-down mouse with an exposed protruding ball. The user rolls the ball
with the thumb, fingers, or the palm of the hand to move a pointer. Compared with a mouse, a trackball
has no limits on effective travel; at times, a mouse can reach an edge of its working area while the operator
still wishes to move the screen pointer farther. With a trackball, the operator just continues rolling, whereas a
mouse would have to be lifted and re-positioned. Some trackballs, such as Logitech's optical-pickoff types,
have notably low friction, as well as being dense (glass), so they can be spun to make them coast. The
trackball's buttons may be situated to that of a mouse or to a unique style that suits the user.

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1.3 Hardware
Laser Mouse:
A mouse allows the user to point by moving the cursor in graphical user interface on a PC’s screen. The
optical mouse actually uses a tiny camera to take 1,500 pictures every second. Able to work on almost any
surface, the mouse has a small, red light-emitting diode (LED) that bounces light off that surface onto
a complementary metal-oxide semiconductor (CMOS) sensor.
The CMOS sensor sends each image to a digital signal processor (DSP) for analysis. The DSP, operating at 18
MIPS (million instructions per second), is able to detect patterns in the images and see how those patterns
have moved since the previous image. Based on the change in patterns over a sequence of images, the DSP
determines how far the mouse has moved and sends the corresponding coordinates to the computer. The
computer moves the cursor on the screen based on the coordinates received from the mouse. This happens
hundreds of times each second, making the cursor appear to move very smoothly.
Sensor:
A sensor measures a specific property data and sends a signal to the computer. They can produce a stream of
input data automatically without any human intervention. Usually this is an analogue signal so it needs to be
converted into digital data for the computer to process. This is done using by an Analogue-to-Digital
Converter (ADC).
Sensors are used extensively in monitoring / measuring / data logging systems, and also in computer control
systems. Following is the list of commonly used sensors:
Temperature
Magnetic Field
Gas
Pressure
Moisture
Humidity
Ph/Acidity/Alkalinity
Motion/ Infra-Red
Advantages of using sensors to collect data are:
1. They can collect data far more frequently than a person.
2. They are more reliable than a person, who may forget to take readings.
3. They are more accurate than a person who may misread the signal.
4. They can collect data from places where it is not possible for a person to go such as inside a chemical
or nuclear reaction vessel.
The disadvantage of using sensors is that they may need a power supply to work and may need regular
calibration to check their accuracy.

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1.3 Hardware
Temperature Sensor:
A temperature sensor produces a signal that depends on the temperature of its surroundings. The computer
process the digitize signal to display a measurement or to control an appliance.
We can use temperature sensor in many appliance such:
Automatic washing machine
Digital thermometer
Controlling heating system in buildings, including greenhouses and chemical reaction vessels.
Pressure sensor:
A pressure sensor produces a signal that depends on the pressure to which it is exposed. Pressure sensor can
be used in many appliances such as automatic blood pressure monitor. Pressure sensor can also control the
pressure of gases or liquids in chemical reaction vessel.
Magnetic Field:
The Magnetic Field Sensor can be used to study the field around permanent magnets, coils, and electrical
devices. This sensor uses a Hall effect transducer, and measures a vector component of the magnetic field near
the sensor tip. It has two ranges, allowing for measurement of relatively strong magnetic fields around
permanent magnets and electromagnets, as well as measurement of weak fields such as the Earth’s magnetic
field. The articulated sensor tip allows you to measure both transverse and longitudinal magnetic fields.
Gas:
A gas sensor produces a signal depending on the concentration of a particular gas or vapor. We can use gas
sensor for an inflammable gas to monitor the atmosphere and sound an alarm if there is a leakage. We can use
gas sensor in other applications such as:
Breathalyser, which measure the concentration of alcohol vapour in a sample of breath and estimate
the concentration of alcohol in blood.
Process control in chemical industry.
Environment monitoring of air pollution.
Moisture/ Humidity sensor
A moisture sensor produces a signal that depends on the concentration of water vapors in the atmosphere. A
moisture sensor can control an irrigation system more efficiently only allow water when soil is dry. We can
use moisture sensor in many other application including:
Controlling a heating system and air conditioning system.
Maintaining sufficient humidity in the air in a greenhouse.
Measuring humidity for meteorological record and forecasting in a weather station.
PH/acidity/alkalinity sensor:

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1.3 Hardware
PH Sensor measures the pH of aqueous solutions in industrial and municipal process applications. It is
designed to perform in the harshest of environments, including applications that poison conventional pH
sensors.
Typical activities using our pH sensor include:
Acid-base titrations
Studies of household acids and bases
Monitoring pH change during chemical reactions or in an aquarium as a result of photosynthesis
Investigations of acid rain and buffering
Analysis of water quality in streams and lakes
Infrared sensor:
An infra (IR) sensor produces a signal that depends on the level of invisible IR radiation falling on it.
All objects (unless they are extremely cold) emit significant IR radiation. Security camera equips with lens
and grid of IR sensors uses this IR radiation to form a detector for a person.

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1.3 Hardware
Output devices
An output device is a piece of hardware that is used to display or output data which has been processed or has
been stored on the computer.
There are many different kind of output devices such as inkjet, laser and 3D printers; 2D and 3D cutters;
speakers and head phones; actuators; flat panel display screens including Liquid Crystal Display (LCD) and
Light-Emitting Diodes (LED); LCD projectors and Digital Light Projectors (DLP)
Printer:
Printer is an output device that prints character and graphics on paper or other materials.
Laser Printer:
Laser printer uses a laser scanning a drum to print with powdered ink, known as toner. The printer places an
even, negative, static charge on a photoconductive drum. It scans a very narrow laser beam across the surface
of the rotating drum. The laser beam causes the negative charge to leak away wherever it shines on the drum.
The drum revolves past a supply of toner which is also charged negatively. The toner is attracted onto those
regions of the drums surface where no charge remains. Toner particles are repelled by those regions that
remain charged because they were not lit by the laser’s beam. The printer rapidly switches the beam on and
off to draw the required pattern of output. A roller presses a sheet of paper against the rotating drum and the
toner particles transfer to the paper.
Another roller presses the paper against a heated ‘fuser’ roller. The heated toner melts and bonds to the paper,
producing a printed copy. If there are four drums with four different colors of toner the printer can print in
color.

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1.3 Hardware
Inkjet printer
An inkjet printer uses a print head to propel differently sized droplets of ink, measuring just picolitres, from a
number of fine nozzles onto a sheet of paper. The printhead scans from side to side on stabilizer bar and
rollers feed the paper forward.

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1.3 Hardware
Speakers:
Speakers are one of the most common output devices used with computer systems. The purpose of speakers is
to produce audio output that can be heard by the listener.
Speakers are transducers that convert electromagnetic waves into sound waves. peakers use magnets to
convert electricity into sound waves. This is a basic principle of physics.
Sound is made when an object makes the particles around it vibrate. These vibrations travel through the air,
and reach your ears. Our brain interprets this motion as sound. High frequencies of sound are made when the
wavelength of the vibrations are close together. Low frequencies occur when they are farther apart. The
amplitude of the vibrations causes the level of volume you hear.
To make these vibrations, speakers have a set of magnets. One of them is called the permanent magnet. It
doesn’t move or change polarity and is made of a magnetic metal like iron. The other magnet is an
electromagnet. It is a coil of metal wire like copper or aluminum. When an electric current is sent through the
electromagnet, it is either attracted to or repelled away from the permanent magnet. The polarity of the coil
can be reversed depending on the current. This back and forth movement causes the diaphragm or cone to
vibrate, because it is connected to the magnetic coil. This is the sound that you hear.

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1.3 Hardware
Actuators:
An actuator is an output device but it does not always provide output directly to the user. It can change some
physical value in response to a signal from an automated system or control system.
Actuators naturally pair up with sensors, which can provide feedback to the control program about the effects
of its actuators.
Backing storage:
Backing storage (also called auxiliary storage) stores programs and data for future use. In order to store data
while the electricity is switched off or unavailable storage must be non-volatile. Access to backing storage is
slower than internal memory. Operating systems and program files are loaded into RAM form backing storage
when required for execution.
It is important to distinguish between a storage device and storage medium. The storage device is the machine
that stores data; the storage medium is the material on which the device stores data. There are three different
types of backing storage device:
1. Magnetic storage device
2. Optical storage device
3. Solid state storage device.
Magnetic Storage device:
Magnetic media stores data by assigning a magnetic charge to metal. This metal is then processed by a read
head, which converts the charges into ones and zeros. Historically, magnetic media has been very popular for
storing programs, data, and making backups. It looks set to continue in this role for some time. However, solid
state technology is starting to be used more and more, storing programs and data on new devices such as
mobile phones and cameras.
Hard disk
Hard disks are usually found inside computers to store programs and data. They are increasingly cheap and
more and more companies are using them to back things up. Hard disks can vary in physical size with some
disks getting as small as your thumb. The capacity of a commercial disk is currently up to about 4 terabytes
allowing users to read and write to them. They are constructed from several key components:

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1.3 Hardware
Platter - Metallic disks where One or both sides of the platter are magnetized, allowing data to be
stored. The platter spins thousands of times a second around the spindle. There may be several
platters, with data stored across them
Head - The head reads magnetic data from the platter. For a drive with several platters there may two
heads per platter allowing data to be read from top and bottom of each
Actuator Arm - used to move the read heads in and out of the disk, so that data can be read and
written to particular locations and you can access data in a Random fashion, you don't need to read
your way through the entire disk to fetch a particular bit of information, you can jump right there.
Seek time is very low.
Power connector - provides electricity to spin the platters, move the read head and run the electronics
IDE connector - allows for data transfer from and to the platters
Jumper block - used to get the disk working in specific ways such as RAID
For the exam you must be able to explain how a hard disk works:
1. The platters spin around the spindle
2. data is requested to be read from a particular area of a platter
3. the actuator arm moves the read head to that track
4. Once the data sector that is required has spun around and under the read head, data is read
5. Read data is sent from the IDE connector to main memory

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1.3 Hardware
Writing data is very similar:
1. The platters spin around the spindle
2. data is sent to the hard disk using the IDE connector
3. the actuator arm moves the write head to the track that will be written to
4. Once the data sector that is required has spun around and under the write head, data is written to the
platter

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1.3 Hardware
Optical media
Optical media works by creating a disc with a pitted metallic surface. There are several different types of disk
out there ranging from 650 MB to 128 GB, with the pits and lands getting closer together for higher volume
disks. The principle behind how each of them works is the same.
Optical media
Device Type Size Image
 CD-ROM
 CD-R
 CD-RW
 Read Only
 Write once then Read only
 re-Writable
650 - 900 MB
 DVD-ROM
 DVD-R
 DVD-RW
 DVD-RAM
 Read Only
 Write once then Read only
 re-Writable
 re-Writable
4.7 - 9.4 GB
 Blu-ray (BD)
disc
 HD DVD
(obsolete)
Re-Writable and Read Only versions available. Uses
a blue laser, that is able to recognise smaller pits and
lands, which allows for the pits and lands to be more
closely packed, and so store more data
25 - 128 GB

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1.3 Hardware
CD-ROM
A CD-ROM is a metal disc embedded into a plastic protective housing. Each disc has to be 'mastered'; this is
the process of creating the CD and placing the data on it. CDs are WORM (Write Once, Read Many) media;
this refers to the fact that once they have been mastered, there is no way to change the data on them.
Writing to a CD-ROM
1. A single track runs in a spiral pattern from the center of the disc to the outside, this track is made of
pits and lands to represent the ones and zeroes of binary data
2. A high-powered laser is shone onto the CD-ROM, burning pits into the metal
3. The disc spins and the laser follows the track, putting the binary data onto the CD in a spiral track
4. The data has been written
Reading from a CD-ROM
1. A single track runs in a spiral pattern from the center of the disc to the outside, this track is made of
pits and lands to represent the ones and zeroes of binary data
2. A low-powered laser is shone on the metallic surface and the reflection is captured in a photodiode
sensor, the lands reflect differently to the pits, meaning it can tell the difference between a 1 and a 0
3. The disc spins and the laser follows the track
4. The binary data (the 1s and 0s) are put together and the CD-ROM has been read

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1.3 Hardware
Solid State Storage Media:
Solid-state memory
Device Description
USB flash drive
Up to 256 GB
Memory card
Up to 256 GB
USB (memory stick) Flash Drive
Internals of a typical USB flash drive
Solid state storage devices are electronic and made as integrated circuits or chip. The currently
predominant technology is flash memory, which like ROM holds data that are non-volatile but can be
erased and rewritten in large blocks. We often refer to this as non-volatile memory.

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1.3 Hardware
1. Put the drive into USB socket.
2. USB driver loads, providing the computer with code on how to read and write from the USB.
3. The USB is read, giving information on the file and folder structure (File Allocation Table) to the
Computer.
4. [Reading] The user chooses to open a file, the Computer sends the address wanted to the USB port.
5. [Reading] The USB returns the data at the location requested.
6. [Writing] The computer sends data to the USB port where it is place into empty space on the drive.
7. [Writing] The computer then requests a new version of the file and folder structure.
Memory cards
Work in much the same way as a Flash drive and can often be converted into Flash Drives. They have
different connectors and are generally smaller than USB Flash drives allowing for them to be used in cameras,
mobile phones and game consoles.

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1.3 Hardware
1.3.2 Main memory
Read only memory (ROM)
ROM holds the instructions for starting up the computer. This type of memory can only be read and cannot be
altered (i.e. deleted or written to) and is non-volatile (i.e. it doesn’t lose its contents when the computer is
switched off).
Programmable read only memory (PROM)
A PROM is a memory chip on which data can be written only once. Once a program has been written onto a
PROM, it is permanent. Unlike RAM, PROM's retain their contents when the computer is turned off. The
difference between a PROM and a ROM (read only memory) is that a PROM is manufactured as a blank
memory, whereas a ROM is programmed during the manufacturing process. To write data onto a PROM chip,
a special device called a PROM programmer or PROM burner is required. Erasable programmable read
only memory (EPROM)
This is a special type of PROM that can be erased by exposing it to ultraviolet (UV) light. Once it has been
erased, it can be re-programmed using an EPROM burner.

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1.3 Hardware
1.3.2 Main memory
Electrically erasable programmable read only memory (EEPROM)
An EEPROM is a special type of PROM that can be erased by exposing it to an electrical charge. Like other
types of PROM, EEPROM retains its contents even when the power is turned off. Also, as with other types of
ROM, EEPROM access time is not as fast as RAM. EEPROMs are similar to flash memories (sometimes
called flash EEPROM). The principal difference is that an EEPROM requires data to be written or erased one
byte at a time, whereas a flash memory allows data to be written or erased in whole blocks. ROM (Read Only
Memory) RAM (Random Access Memory) PROM – Programmable Read Only Memory EPROM – Erasable
Programmable Read Only Memory EEPROM – Electrically Erasable Programmable Read Only Memory
SRAM (Static RAM) DRAM (Dynamic RAM)
Random access memory (RAM)
This is a volatile memory (i.e. contents are lost when the computer is switched off). A user can write or delete
data as well as read the contents. Before a program can be ran it must first be loaded into RAM which allows
the CPU to access the program. Battery-backed RAMs overcome data loss on switching power off, but are
outside the scope of these booklets.
(NOTE: For completeness, it is worth mentioning that two types of RAM exist called SRAM (static RAM)
and DRAM (dynamic RAM) – SRAM doesn’t need to be constantly refreshed to retain its memory unlike
DRAM. Also note that computers use cache which is a portion of memory made from SRAM. Memory
caching works since programs usually access the same data or instructions over and over again. By retaining
as much information as possible in SRAM, the computer operates more quickly (cache is usually termed level
1, 2 or 3 (termed L1, L2 or L3)).

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1.3 Hardware
1.3.3 Logic gates and logic circuits
Introduction to Logic
Many electronic circuits operate using binary logic gates. Logic gates basically process signals which
represent true or false or the equivalent i.e. ON or OFF, 1 or 0
Whilst there are a number of logic gates, only the six simplest are covered in this booklet: NOT gate, AND
gate, OR gate, NAND gate, NOR gate and XOR.
The following notes describe the function of all six gates, how to produce truth tables, how to design networks
using logic gates, and how to determine the output from a logic network.
The six main logic gates
The most common symbols used to represent logic gates are shown below. To avoid confusion the graphical
representations will be used in exam questions but candidates may use either set of symbols when answering
questions.
Simple graphical representation
Symbols used to represent logic gates
A Truth Table is simply a table listing all the combinations of inputs and their respective outputs.
The NOT gate has only one input, but the rest have 2 inputs.
AND OR NOT
C
NAND
NOR
XOR

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1.3 Hardware
The next section describes the function of all six logic gates.
Name Symbol Logic Truth Table
NOT GATE
The output (called X) is
true (i.e.1 or ON) when the
INPUT A is NOT
TRUE (i.e. 0 or OFF)
AND GATE
The output is only true
(i.e.1 or ON) when the
(INPUT A AND INPUT B)
are both TRUE
(i.e. 0 or OFF)
OR GATE
The output is true
(i.e.1 or ON) if (INPUT A
OR INPUT B) are TRUE
(i.e. 0 or OFF)
NAND GATE
This is basically an AND
gate with the output inverted
The output is true(i.e.1 or
ON) if (INPUT A AND
INPUT B) are NOT both
TRUE (i.e. 0 or OFF)
NOR GATE
This is basically an OR gate
with the output inverted
The output is true (i.e.1 or
ON) if NOT(INPUT A
AND INPUT B) are TRUE
EXCLUSIVE-
OR GATE
(XOR GATE)
The output is true only
when the inputs are opposite
of each other

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1.3 Hardware
The tables above containing 1s and 0s are known as truth tables and are an integral part of logic gates
functionality. These are used extensively throughout this booklet in the design and testing of logic networks
built up from logic gates.
Combinations of logic gates
It is possible to combine logic gates together to produce more complex logic networks.
This booklet will only deal with a maximum of three inputs and up to six logic gates. The output from a logic
network is checked by producing the truth table (as shown in the examples below).
We will deal with two different scenarios here. The first involves drawing the truth table from a given logic
network; the second involves designing a logic network for a given problem and then testing it by drawing the
truth table.
Producing the truth table from a given logic network
Consider the following logic network which contains three inputs and three logic gates:
If we now look at the output in two stages. First let us consider the outputs being produced at stages S and T.
To do this we need to draw a truth table. There are three inputs (A, B and C) which gives 23 (i.e. 8) possible
combinations of 1s and 0s. To work out the outputs at S and T we need to refer to the truth tables for the NOR
gate and for the AND gate. For example, when A = 1 and B = 1 then we have 1 NOR 1 which gives the value
of S = 0. Continuing doing the same thing for all 8 possible inputs we get the following interim truth table:

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1.3 Hardware
Designing logic networks to solve a specific problem and testing using truth tables
Consider the following problem:
“If button A or button B are on and button C is off then the alarm X goes on”
We can convert this onto logic gate terminology (ON = 1 and OFF = 0):
If (A = 1 OR B = 1) AND (C = NOT 1) then (X = 1)
(Notice: rather than write 0 we use NOT 1)

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1.3 Hardware
To draw the logic network, we do each part in brackets first i.e. A = 1 OR B = 1 is one gate then C = NOT 1 is
the second gate. These are then joined together by the AND gate. Once the logic network is drawn we can
then test it using a truth table. Remember the original problem – we are looking for the output to be 1 when A
or B is 1 and when C is 0. Thus we get the following logic network and truth table from the network. Looking
at the values in the truth table, we will be able to clearly see that it matches up with the original problem
which then gives us confidence that the logic network is correct.
X

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1.3 Hardware
Let us now consider a second problem:
A steel rolling mill is to be controlled by a logic network made up of AND, OR and NOT gates only. The mill
receives a stop signal (i.e. S = 1) depending on the following input bits:
A stop signal (S = 1) occurs when:
either Length, L > 100 metres and Velocity, V < 10 m/s
or Temperature, T < 1000 C and Velocity, V > 10 m/s
Draw a logic network and truth table to show all the possible situations when the stop signal could be
received.
The first thing to do is to try and turn the question into a series of logic gates and then the problem becomes
much simplified.
The first statement can be re-written as: (L = 1 AND V = NOT 1) since Length > 100 metres
corresponds to a binary value of 1 and Velocity < 10 m/s corresponds to a binary value of 0 (i.e. NOT
1).
The second statement can be re-written as (T = NOT 1 AND V = 1) since Temperature < 1000C
corresponds to a binary value of 0 (i.e. NOT 1) and Velocity > 10 m/s corresponds to a binary value
of 1
Both these statements are joined together by OR which gives us the logic statement:
if (L = 1 AND V = NOT 1) OR (T = NOT 1 AND V = 1) then S = 1
We can now draw the logic network and truth table to give the solution to the original problem (input L has
been put at the bottom of the diagram just to avoid crossing over of lines; it merely makes it look neater and
less complex and isn’t essential):

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1.3 Hardware
Other Questions:
In questions 1 to 6, produce truth tables from the given logic networks. Remember that if there are TWO
inputs then there will be four (22) possible outputs and if there are THREE inputs there will be eight (23)
possible outputs.
i.e.

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1.3 Hardware

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1.3 Hardware
Questions 7 to 10 require both the logic network to be created and also the truth table. The truth table can be
derived from the logic network, but also from the problem. This is a check that the logic network actually
represents the original problem.
(7) A computer will only operate if three switches P, S and T are correctly set. An output signal
(X = 1) will occur if P and S are both ON or if P is OFF and S and T are ON. Design a logic network and
draw the truth table for this network.
(8) A traffic signal system will only operate if it receives an output signal (D = 1). This can only occur if:
either (a) signal A is red (i.e. A = 0)
or (b) signal A is green (i.e. A = 1) and signals B and C are both red (i.e. B and C are both 0)
Design a logic network and draw a truth table for the above system.

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1.3 Hardware
(9) A chemical plant gives out a warning signal (W = 1) when the process goes wrong. A logic network is
used to provide input and to decide whether or not W = 1.
A warning signal (W = 1) will be generated if
either (a) Chemical Rate < 10 m3/s
or (b) Temperature > 87 C and Concentration > 2 moles
or (c) Chemical rate = 10 m3/s and Temperature > 87 C
Draw a logic network and truth table to show all the possible situations when the warning signal could be
received.
(10) A power station has a safety system based on three inputs to a logic network. A warning signal (S = 1)
is produced when certain conditions occur based on these 3 inputs:
A warning signal (S = 1) will be generated if:
either (a) Temperature > 120C and Cooling Water < 100 l/hr
or (b) Temperature < 120C and (Pressure > 10 bar or Cooling Water < 100 l/hr)
Draw a logic network and truth table to show all the possible situations when the warning signal could be
received.

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1.4 Processor fundamentals
1.4.1 CPU architecture
The Von Neumann Architecture
The earliest computing machines had fixed programs. For example, a desk calculator (in principle) is a fixed
program computer. It can do basic mathematics, but it cannot be used as a word processor or a gaming
console. Changing the program of a fixed-program machine requires re-wiring, re-structuring, or re-designing
the machine. The earliest computers were not so much "programmed" as they were "designed".
"Reprogramming", when it was possible at all, was a laborious process, starting with flowcharts and paper
notes, followed by detailed engineering designs, and then the often-arduous process of physically re-wiring
and re-building the machine. It could take up to 3 weeks to set up a program on ENIAC (a computer of 1940s)
and get it working.
The phrase Von Neumann architecture derives from a paper written by computer scientist John von Neumann
in1945. This describes a design architecture for an electronic digital computer with subdivisions of a central
arithmetic part, a central control part, a memory to store both data and instructions, external storage, and input
and output mechanisms. The meaning of the phrase has evolved to mean “A stored-program computer”. A
stored-program digital computer is one that keeps its programmed instructions, as well as its data, in read-
write, random-access memory (RAM). So John Von Neumann introduced the idea of the stored program.
Previously data and programs were stored in separate memories. Von Neumann realized that data and
programs are somewhat of the same type and can, therefore, use the same memory. On a large scale, the
ability to treat instructions as data is what makes assemblers, compilers and other automated programming
tools possible. One can "write programs which write programs". This led to the introduction of compilers
which accepted high level language source code as input and produced binary code as output.

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The Von Neumann architecture uses a single processor which follows a linear sequence of fetch-decode-
execute. In order to do this, the processor has to use some special registers, which are discrete memory
locations with special purposes attached. These are
Register Meaning
PC Program Counter
CIR Current Instruction Register
MAR Memory Address Register
MDR Memory Data Register
Status A General Purpose Register
IX Index Register
Accumulator Holds results
>>Program counter (PC): Keeps track of where to find the next instruction so that a copy of the instruction
can be placed in the current instruction register. Sometimes the program counter is called the Sequence
Control Register (SCR) as it controls the sequence in which instructions are executed.
>>Current instruction register (CIR):Holds the instruction that is to be executed.
>>Memory address register (MAR): Used to hold the memory address that contains either the next piece of
data or an instruction that is to be used.
>>Memory data register (MDR): Acts like a buffer and holds anything that is copied from the memory
ready for the processor to use it.
>>Index register (IR): A microprocessor register used for modifying operand addresses during the run of a
program, typically for doing vector/array operations. Index registers are used for a special kind of indirect
addressing (covered in 3.5 (i) ) where an immediate constant (i.e. which is part of the instruction itself) is
added to the contents of the index register to form the address to the actual operand or data.

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>>Status Register (General purpose register): It sits inside ALU and has following three purposes/uses
during a programs' instructions execution.
It holds:
1) Results of comparisons to decide later for action.
2) Interim results of arithmetic performed
3) Any errors occurred during the arithmetic operations, like overflow etc.
The central processor contains the arithmetic-logic unit (also known as the arithmetic unit) and the control
unit. The arithmetic-logic unit (ALU) is where data is processed. This involves arithmetic and logical
operations. Arithmetic operations are those that add and subtract numbers, and so on. Logical operations
involve comparing binary patterns and making decisions.
The control unit fetches instructions from memory, decodes them and synchronizes the operations before
sending signals to other parts of the computer.
The accumulator is in the arithmetic unit, the Program counter (PC) and the Instruction registers (CIR) are in
the control unit and the memory data register(MDR) and memory address register(MAR) are in the
processor.

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A typical layout is shown in Fig. 3.3.a.1 which also shows the data paths.
Main Memory
Fig 3.3.a.1
Central Processing Unit (CPU)
ALU
Accumulator
Control Unit
PC
CIR
MDR
MAR

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Arithmetic logic unit
A simple example of an arithmetic logic unit (2-bit ALU) that does AND, OR, XOR, and addition
The Arithmetic Logic Unit or the ALU is a digital circuit that
performs arithmetic and logical operations. Where arithmetic
operations include things such as ADDITION and SUBTRACTION
and the logical operations include things such as AND, OR, NOT.
The ALU is a fundamental building block in the central processing
unit (CPU) of a computer and without it the computer wouldn't be
able to calculate anything!

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Some examples of assembly code instructions that would use the ALU are as follows (not all processors will
have all these instructions):

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Control unit - sits inside the CPU and coordinates the input and output devices of a computer system. It
coordinates the fetching of program code from main memory to the CPU and directs the operation of the other
processor components by providing timing and control signals.
Processor clock-is a timing device connected to the processor that synchronizes when the fetch, decode
execute cycle runs
Your computer might contain several clocks thatregulate different things. The clock we are going to look at
here will keep the processor in line. It will send the processor a signal at regular times telling it to start the
fetch decode execute routine.
Lights flash atfrequencies of 0.5 Hz, 1.0 Hz and 2.0 Hz, where Hz means flashes per second. (Hz= Hertz,
S.I unit of frequency)
Clock speed - The number of cycles that are performed by the CPU per second
Clock speed is measured in Hertz, which means 'per second'. You have probably heard of clock speeds such as
1 MHz, this means 1,000,000 cycles per second and potentially a million calculations. A computer of speed
3.4 GHz means it might be capable of processing 3,400,000,000 instructions per second! However it isn't as
simple at that, some processors can perform more than one calculation on each clock cycle, and processors
from different manufacturers and using different architecture are often difficult to compare. (See
the Megahertz myth). Also with the increase in multi-core processors such as the PS3 (7 cores) and the Xbox
360 (3 cores) there might be times where the clock might be ticking but there is nothing for the processor to
calculate, the processor will then sit idle.

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Data, Address and Control Buses
A bus is a set of parallel wires connecting two or more components of the computer.
The CPU is connected to main memory by three separate buses. When the CPU wishes to access a particular
memory location, it sends this address to memory on the address bus. The data in that location is then returned
to the CPU on the data bus. Control signals are sent along the control bus.
In Figure below, you can see that data, address and control buses connect the processor, memory and I/O
controllers. These are all system buses. Each bus is a shared transmission medium, so that only one device can
transmit along a bus at any one time.
Data and control signals travel in both directions between the processor, memory and I/O controllers. Address,
on the other hand, travel only one way along the address bus: the processor sends the address of an instruction,
or of data to be stored or retrieved, to memory to an I/O controller.
The control bus is a bi-directional bus meaning that signals can be carried in both directions. The data and
address buses are shared by all components of the system. Control lines must therefore be provided to ensure
that access to and use of the data and address buses by the different components of the system does not lead to
conflict. The purpose of the control bus is to transmit commands, timings and specific status information
between system components. Timing signals indicate the validity of data and address information.
Command signals specify operations to be performed. Specific status signals indicate the state of a data
transfer request, or the status of request by a component to gain control of the system bus.
The data bus, typically consisting of 8, 16, or 32 separate lines provides a bi-directional path for moving data
and instructions between system components. The width of the data bus is a key factor in determining overall
system performance.
For example, if the data bus is 8 bits wide, and each instruction is 16 bits long, then the processor must access
the main memory twice during each instruction cycle.
Address bus: When the processor wishes to read a word (say 8, 16, or 32 bits) of data from memory, it first
puts the address of the desired word on the address bus. The width of the address bus determines the
maximum possible memory capacity of the system. For example, if the address bus consisted of only 8 lines,
then the maximum address it could transmit would be (in binary) 11111111 or 255 – giving a maximum

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memory capacity of 256 (including address 0). A more realistic minimum bus width would be 20 lines, giving
a memory capacity of 220
, i.e. 1Mb.
Increasing performance
If we want to increase the performance of our computer, we can try several things
Increasing the clock speed
Adjusting word length
Increasing bus widths
For each different method, we are going to look at these old games consoles to see how performance increase
was achieved:
System Year Speed Word size Notes
NES 1983 1.79 MHz 8 bit
SNES 1990 3.58 MHz 16 bit
Nintendo 64 1996 93.75 MHz 64 bit
GameCube 2001 486 MHz 128 bit cooling fan introduced

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Clock speed - The number of cycles that are performed by the CPU per second
The most obvious way to increase the speed of a computer would be to increase the speed of the computer
clock. With a faster clock speed the processor would be forced to perform more instructions per second.
But what is to stop us increasing the clock speed as much as we want? If you study Physics you might already
know this, but the problem with increased clock speed is that an increased current will have to flow through
the circuits. The more current that flows through a circuit, the more heat will be generated. You might notice
that a laptop will get hot or even your mobile phone when you are doing a heavy task like playing a game. The
faster the clock speed, the hotter the processor runs.
To counter this issue, computer scientists have come up with more advance chip designs and introduced heat
sinks, fans, and even liquid cooling into computers. If a processor runs too hot it can burn out!

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Peripherals
Input/output devices are used by the system to get information in and out, as they are not internal but are
connected to the CPU, we refer to them as peripherals (your hands are peripheral to your torso). We'll cover
the specific ones you need to learn a little later, but for the moment you need to know the fundamental
difference:
Input Devices - used to feed information to the system. E.g. Keyboard
Output Devices - An output device is used to display the results of data processing on the input data.
E.g. Visual Display Unit (VDU)
If you look at the Von Neumann Architecture notice that it doesn't mention Keyboard or display, this was a
very well thought out action, as you don't want to force every computer to have a keyboard (think about a
games console) or a VDU (some devices such as MP3 players don't have a screen like the iPod Shuffle).
However, some computer architecture does include specific I/O controllers:
I/O controllers- an electronic circuit that connects to a system bus and an I/O device; it provides the correct
voltages and currents for the system bus and the I/O device. Examples would include:
keyboard controller, attached to a keyboard
disk controller for a Hard Disk (Hard Disks are not main memory!)
video display controller, attaching a video display unit (monitor)
I/O port - a complementary method of performing input/output between the CPU and peripheral devices in a
computer. This allows I/O devices to be connected to the CPU without having to have specialized hardware
for each one. Think about the USB port on your computer, you can connect Keyboards, Mice, Game pads,
Cameras, Phones, etc. and they all connect using the same type of port!

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1.4.2 The fetch-execute cycle
The process by which a computer:
1. Fetches a program instruction from its memory,
2. determines what instruction wants to do,
3. And execute those actions.
This cycle is repeated continuously by the central processing unit (CPU), from bootup to shut down. In
modern computers this means completing the cycle billions of times in a second! Without it, nothing would be
able to be calculated.
Registers involved
The circuits used in the CPU during the cycle are:
Program Counter (PC) - an incrementing counter that keeps track of the memory address of which
instruction is to be executed next...
Memory Address Register (MAR) - the address in main memory that is currently being read or
written
Memory Data Register (MDR) - a two-way register that holds data fetched from memory (and data
ready for the CPU to process) or data waiting to be stored in memory
Current Instruction register (CIR) - a temporary buffer for the instruction that has just been fetched
from memory
Control Unit (CU) - decodes the program instruction in the CIR, selecting machine resources such as
a data source register and a particular arithmetic operation, and coordinates activation of those
resources
Arithmetic logic unit (ALU) - performs mathematical and logical operations

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Register notation
To describe the cycle we can use register notation. This is a very simple way of noting all the steps involved.
In all cases where you see brackets e.g. [PC], this means that the contents of the thing inside the brackets are
loaded. In the case of the first line, the contents of the program counter are loaded into the Memory Address
Register.
(Increment the PC for next cycle at the
same time)
Decoded then executed
Detailed description of Fetch-Decode-Execute Cycle
To better understand what is going on at each stage we'll now look at a detailed description:
1. The contents of the Program Counter, the address of the next instruction to be executed, is placed into
the Memory Address Register

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2. The address is sent from the MAR along the address bus to the Main Memory. The instruction at that
address is found and returned along the data bus to the Memory Buffer Register. At the same time the
contents of the Program Counter is increased by 1, to reference the next instruction to be executed.
.
3. The MBR loads the Current Instruction Register with the instruction to be executed.
4. The instruction is decoded and executed using the ALU if necessary.
The Cycle starts again!

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1.4.3 The processor’s instruction set
Instruction set - the range of instructions that a CPU can execute
There are many different instructions that we can use in machine code, you have already met three (LDA,
ADD, STO), but some processors will be capable of understanding many more. The selection of instructions
that a machine can understand is called the instruction set. Below is a list of some other instructions that might
be used:

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You'll notice that in general, instructions have two main parts:
opcode - instruction name
operand - data or address
Depending on the word size, there will be different numbers of bits available for the opcode and for the
operand. There are two different philosophies at play, with some processors choosing to have lots of different
instructions and a smaller operand (Intel, AMD) and others choosing to have less instructions and more space
for the operand (ARM).
CISC - Complex Instruction Set Computer - more instructions allowing for complex tasks to be
executed, but range and precision of the operand is reduced. Some instruction may be of variable
length, for example taking extra words (or bytes) to address full memory addresses, load full data
values or just expand the available instructions.
RISC - Reduced Instruction Set Computer - less instructions allowing for larger and higher precision
operands.

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Memory Addressing Modes, an Introduction
There are many ways to locate data and instructions in memory and these methods are called 'memory address
modes'
Memory address modes determine the method used within the program to access data either from within the
CPU or external RAM. Some memory addressing modes can control program flow.
The five memory address modes are
Direct
Indirect
Immediate
Indexed
Relative
Immediate Addressing
Immediate addressing means that the data to be used is hard-coded into the instruction itself.
This is the fastest method of addressing as it does not involve main memory at all.
For example, you want to add 2 to the content of the accumulator
The instruction is:
ADD #2
Nothing has been fetched from memory; the instruction simply adds 2 to the accumulator
immediately.
Immediate Addressing is very useful to carry out instructions involving constants (as opposed to
variables). For example you might want to use 'PI' as a constant 3.14 within your code.

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Direct (or Absolute) Addressing
This is a very simple way of addressing memory - direct addressing means the code refers directly to
a location in memory
For example
SUB (3001)
In this instance the value held at the absolute location 3001 in RAM is subtracted from the
accumulator.
The good thing about direct addressing is that it is fast (but not as fast as immediate addressing) the
bad thing about direct addressing is that the code depends on the correct data always being present at
same location.
It is generally a good idea to avoid referring to absolute memory addresses in order to have 're-
locatable code' i.e. code that does not depend on specific locations in memory.
You could use direct addressing on computers that are only running a single program. For example
an engine management computer only ever runs the code the car engineers programmed into it, and
so direct memory addressing is excellent for fast memory access.
Indirect Addressing
Indirect addressing means that the address of the data is held in an intermediate location so that the
address is first 'looked up' and then used to locate the data itself.
Many programs make use of software libraries that get loaded into memory at run time by the loader.
The loader will most likely place the library in a different memory location each time.
So how does a programmer access the subroutines within the library if he does not know the starting
address of each routine?
Answer: Indirect Addressing

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It works like this
1. A specific block of memory will be used by the loader to store the starting address of every
subroutine within the library. This block of memory is called a 'vector table'. A vector table holds
addresses rather than data. The application is informed by the loader of the location of the vector
table itself.
2. In order for the CPU to get to the data, the code first of all fetches the content at RAM location
5002 which is part of the vector table.
3. The data it contains is then used as the address of the data to be fetched, in this case the data is at
location 9000
A typical assembly language instruction would look like
MOV A, @5002
This looks to location 5002 for an address. That address is then used to fetch data and load it into the
accumulator. In this instance it is 302.

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Indexed Addressing
Indexed addressing means that the final address for the data is determined by adding an offset to a
base address.
Very often, a chunk of data is stored as a complete block in memory.
For example, it makes sense to store arrays as contiguous blocks in memory (contiguous means
being next to something without a gap). The array has a 'base address' which is the location of the
first element, then an 'index' is used that adds an offset to the base address in order to fetch any other
element within the array.
Index addressing is fast and is excellent for manipulating data structures such as arrays as all you
need to do is set up a base address then use the index in your code to access individual elements.
Another advantage of indexed addressing is that if the array is re-located in memory at any point
then only the base address needs to be changed. The code making use of the index can remain
exactly the same.

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Relative Addressing
Quite often a program only needs to jump a little bit in order to jump to the next instruction. Maybe
just a few memory locations away from the current instruction.
A very efficient way of doing this is to just add a small offest to the current address in the program
counter. (Remember that the program counter always points to the next instruction to be executed).
This is called 'relative addressing'
DEFINITION:
Relative addressing means that the next instruction to be carried out is an offset number of
locations away, relative to the address of the current instruction.
Consider this bit of pseudo-code:
jump +3 if accumulator == 2
code executed if accumulator is NOT = 2
jmp +5 (unconditional relative jump to avoid the next line of code)
acc:
code executed if accumulator is = 2)
carryon:
In the code snippet above, the first line of code is checking to see if the accumulator has the value of
2 in it. If it is has, then the next instruction is 3 lines away. This is called a conditional jump and it
is making use of relative addressing.
Another example of relative addressing can be seen in the jmp +5 instruction. This is telling the CPU
to effectively avoid the next instruction and go straight to the 'carryon' point.

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Summary of memory modes
Memory modes
Type Comment
Immediate Apply a constant to the accumulator. No need to access main memory
Direct or
Absolute
addressing
This is a very simple way of addressing memory - the code refers directly to a
location in memory. Disadvantage is that it makes relocatable code more
difficult.
Indirect
Addressing
Looks to another location in memory for an address and then fetches the data
that is located at that address. Very handy of accessing in-memory libraries
whose starting address is not known before being loaded into memory
Indexed
Addressing
Takes a base address and applies an offset to it and fetches the data at that
address. Excellent for handling data arrays
Relative
Addressing
Tells the CPU to jump to an instruction that is a relative number of locations
away from the current one. Very efficient way of handling program jumps and
branching.

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1.4.4 Assembly language
Machine code - simple instructions that are executed directly by the CPU
As we already know from chapter 1, computers can only understand binary, 1s and 0s. We are now going to
look at the simplest instructions that we can give a computer. This is called machine code.
Machine code allows computers to perform the most basic, but essential tasks. For this section we are going to
use the Accumulator (you met this register earlier) to store the intermediate results of all our calculations.
Amongst others, the following instructions are important for all processors:
LDD - Loads the contents of the memory address or integer into the accumulator
ADD - Adds the contents of the memory address or integer to the accumulator
STO - Stores the contents of the accumulator into the addressed location
Assembly code is easy to read interpretation of machine code, there is a one to one matching; one line of
assembly equals one line of machine code:
Machine code Assembly code
000000110101 = Store 53
Let's take a look at a quick coding example using assembly code.
LDM #23: Loads the number 23 into the accumulator.
ADD #42: Adds the number 42 to the contents of the accumulator = 65.
STO 34: Saves the accumulator result to the memory address 34.
The code above is the equivalent of saying x = 23 + 42 in VB language.

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Addressing modes
You might notice that some instructions use”#” and others don't, you might even have an inkling as to what
the difference is. Well here is the truth:
# = number
[No hash] = address
Let's take a look at a quick example:
Assembly code Main memory start Main memory end
LDM #10
ADD #12
STORE 12
Address Contents
10 9
11 2
12 7
13 10
14 12
Address Contents
10 9
11 2
12 22
13 10
14 12
This code loads the number 10 into the accumulator, then adds the number 12, it then stores the result 22
into memory location 12.

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Let's take a look at doing this without the hashes:
Assembly code Main memory start Main memory end
LDD 10
ADD12
STORE 12
Address Contents
10 9
11 2
12 7
13 10
14 12
Address Contents
10 9
11 2
12 16
13 10
14 12
This code loads the value stored in memory location 10 into the accumulator (9), then adds the value stored in
memory location 12 (7), it then stores the result into memory location 12 (9 + 7 = 16).

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Machine code and instruction sets
There is no set binary bit pattern for different opcodes in an instruction set. Different processors will use
different patterns, but sometimes it might be the case that you are given certain bit patterns that represent
different opcodes. You will then be asked to write machine code instructions using them.
Below is an example of bit patterns that might represent certain instructions.
Machine code Instruction Addressing mode Hexadecimal Example
0000 STORE Address 0 STO 12
0001 LOAD Number 1 LDM #12
0010 LOAD Address 2 LDD 12
0100 ADD Number 4 ADD #12
1000 ADD Address 8 ADD 12
1111 HALT None F END

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1.5 System software
1.5.1 Operating system
An operating system is simply a set of programs designed to run in the background on a computer system,
giving an environment in which application software can be executed.
Most operating systems consist of a large set of programs, only some of which are stored in the processor
memory all of the time. Many of the subroutines available in the O.S. are stored on the hard drive so that they
can be accessed when needed. This not only saves space in the processor memory but also means that the O.S.
can be easily replaced when needed.
When you are using an applications package you are not communicating with the computer hardware, you are
communicating with the operating system. Without an operating system, no matter how many programs you
have, the computer is useless. The operating system sits between the hardware and the application program or
user.
The operating system is likely to be stored on a backing store (Hard-Drive) rather than in the memory of the
computer (RAM) because:
1. The OS requires a large amount of storage space.
2. It allows for easy upgrading or changing from one system to another one.
Summary:
1. Operating system is a software program which controls the operations of the computer system.
2. It provides a user interface.
3. It controls how the computer responds to user’s requests
4. It controls how the hardware communicate with each other
5. It provides an environment in which application software can be executed

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1.5 System software
Types of Operating System
Batch Processing:
When computing was still a new science, there were not enough machines to satisfy the demand for processor
time from students in universities who wanted great calculations done, firms who wanted their payroll worked
out, and many others. The big problem was the ‘speed mismatch’ between the user sitting at the keyboard who
was very slow, and the machine which was very fast. This meant that the expensive part, the computer, was
sitting there doing nothing while the human being decided what to do. There are two simple solutions to this
problem, one is to buy more machines and the other is to make the machines work more effectively by taking
away the slowest part of the system “the human being”. Nowadays we might well opt to buy more machines,
but was too costly in the past. This problem gave rise to the development of batch processing.
A Batch processing OS is one that does not allow for interaction between the user and the processor during the
execution of the work. Lots of programs or data that need to be run are collected together (to form a batch)
and they are sent to the computer in one go. The batch operating system then controls their passage through
the computer.
Nowadays, batch processing tends to be used where:
Processing cannot be started until all the data is collected
Large amounts of data to be processed,
The data is very similar in nature and…
Requires similar processing,
The computer system has identifiable times when it is not being used, and so has available processor time
The application does not require human intervention.
Applications of the Batch processing OS:
In banks for the production of bank statements from customer files
The production of utility bills from customer records
Compilation of high level language programs where a number of users want programs compiled.

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1.5 System software
Real-time processing:
A real-time O.S. is one which can react quickly enough to aprocess and get ready for the next input or process
to be carried out.
Most real-time systems are based on control of some process in the real world or on information handling.
Real time process control is a real time system. But this is very different to real time (transaction) processing;
this system usually involves sensors and feedback loops i.e. the output can influence the next input to the
system.
Sensors send data (via an analogue to digital converter – ADC) to a computer or microprocessor which
decides whether or not to take action (based on comparison with stored data). If a change needs to be made,
the computer/microprocessor sends signals (via a digital to analogue converter – DAC) to the devices being
controlled and alters their status (e.g. turn a heater on if a temperature sensor indicates that a temperature is
too low) – actuators are often used to open valves, turn on equipment, etc. As this is continuously monitored,
eventually the temperature will equal the stored value in the computer/microprocessor – this will then cause
the heater to be turned off. A chemical plant has a reaction vessel where the temperature is critical to the result
of the process. The temperature is monitored by a computer which accepts input from a sensor and then makes
a decision whether to adjust the heating elements in the vessel. In this example, it would not be sensible for
the computer to be running any O.S. that is not real-time because if there was a delay in the decision making
process, it might negatively affect the reactor. A robot trolley is controlled by a processor which takes input
from a sensor following a black line on the floor, and makes decisions concerning steering to keep the trolley
on the black line. If the processor was not controlled by a real-time O.S, the trolley would go off track because
it wasn’t steering quickly enough.
In real time (transaction) processing files are often updated in real time (e.g. when booking flights on an
airplane); In real time process control, physical quantities (such as temperature) are continuously monitored
and the input is processed quick enough to be capable of influencing the data source. A catalogue shop
processes orders by the barcode for a product being input and the system then comparing the code with
information in its files on the database. When it finds the correct code it can report to the user the quantity of
that item that there are in stock. If there was only one left of a certain item, it would be necessary to record the
fact that a shopper had bought it before the next shopper has their request sent otherwise the two shipments
might get mixed up and cause problems. Because the information on the system must be processed
immediately, O.S needs to be ready to handle input as soon as it comes in. This means that it can’t be sitting
idle while it is waiting for user input. This implies that the computer will not be at its full potential as far as
processing is concerned. When this happens, it is said to display a high rate of redundancy. Real-time
systems tend to display a high rate of redundancy.

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1.5 System software
Single User:
As the term implies, a single user O.S. is specifically one that is used to control a system which has only one
user, and their programs, at any one time. A perfect example of a single user system is the one that you may
have at home. Only one person uses it at a time. Most single user systems are also multi-tasking.
Multi-tasking:
This is a type of O.S. that allows several applications to be available simultaneously. On a simple single user
system you will probably be used to having a number of things running at the same time. Perhaps one window
shows a spreadsheet while another shows a word processing application. You may decide to copy the sheet
from the spreadsheet software to the word-processed document. It appears that more than one task is running
simultaneously. They aren’t, they just appear to be. The O.S. that most of us use on our own computer
systems, Windows, is a multi-tasking O.S.
Application programs nowadays also run many different tasks in multi-tasking operating system environment.
So it is not necessary that only end users multi-task but programmers can also develop applications that
require multitasking.
Multi-user:
Again, as the name implies, this type of O.S services more than one user simultaneously. There are two types
of multi-user O.S:
1. A network system comprises of a number of computers linked together for the purposes of communication
and sharing of resources. Normally, one of the machines is used to control the rest of the system; this machine
is called the server. Networks are important because they allow hardware and software to be shared and also
means that a single copy of the information on a system is needed, and so can be kept up to date relatively
easily.
2. A time-sharing system has a single (normally powerful) computer which is connected up to a number of
terminals. These terminals are not computers as in the case of the network system, but have a very limited
amount of processing power. Again, such a system allows communication between users on the system and
also allows sharing of hardware and software resources across the system.
At the moment it is difficult to tell the difference between the two types of multi-user system, but be careful
because a network system is not really a multi user system as each computer is only being used by one person
at a time. We shall return to this in chapter 3.1.

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1.5 System software
Distributed:
A distributed system is one that allows software and data files to be distributed around a system. An ordinary
network will have a server controlling it and the access to the hard drive, which is connected to the server. A
distributed system might store the word processing software on one computer’s hard drive, while the files of
work are stored somewhere else, and the spreadsheet software is stored on a third disk drive. This can speed
access to files because there is no single bottle neck which all the information must pass through; however the
security and maintenance of the system are more complicated. Another type of distributed system is to
distribute the entire programs and data to more than one place on the network. This speeds up access to the
data but means that if data is updated on one part of the system it may not be on others, which means that the
different versions of the data need to be compared and amended on a regular basis.
Applications requiring batch processing
Utility billing system: The consumption units’ data of the utilities is gathered for a particular time
and then processed altogether and bills are generated.
Payroll: The attendance, loans, taxes and other salary related data is collected for the whole month (or
for predefined period) and payroll is run at the end to distribute salaries.
Backing up: Making a backup of day long transactions at the end of the day: For example, the log of
all transactions happened during the day at a bank are backed up during night time.
Applications requiring online processing
Health monitoring systems: At the hospital, emergency machines monitor the health condition in
real time and let the attendant, or doctor know about any sudden emergencies that may arise.
Process Control: Process control is a statistics and engineering discipline that deals with
architectures, mechanisms, and algorithms for controlling the output of a specific process. (See also
control theory)
For example, heating up the temperature in a room is a process that has the specific, desired outcome to reach
and maintain a defined temperature (e.g. 20°C), kept constant over time. Here, the temperature is the
controlled variable. At the same time, it is the input variable since it is measured by a thermometer and used to
decide whether to heat or not to heat. The desired temperature (20°C) is the set point. The state of the heater
(e.g. the setting of the valve allowing hot water to flow through it) is called the manipulated variable since it is
subject to control actions.
Point of Sale System (POSs): Point of sale (POS) or checkout is the location where a transaction
occurs. A "checkout" refers to a POS terminal or more generally to the hardware and software used
for checkouts, the equivalent of an electronic cash register.
A POS terminal manages the selling process by a salesperson accessible interface. The same system allows
the creation and printing of the receipt.

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1.5 System software
ATM machine process control: An automated teller machine (ATM), also known as a Cash Machine
and by several other names, is a computerized telecommunications device that provides the clients of
a financial institution with access to financial transactions in a public space without the need for a
cashier, human clerk or bank teller. On most modern ATMs, the customer is identified by inserting a
plastic ATM card with a magnetic stripe or a plastic smart card with a chip, which contains a unique
card number and some security information such as an expiration date. Authentication is provided by
the customer entering a personal identification number (PIN code).
Using an ATM, customers can access their bank accounts in order to make cash withdrawals, credit card cash
advances, and check their account balances as well as purchase prepaid cell phone credit.
Types of User Interface
A computer is used by a person who needs to communicate with the machine in order to instruct it as to their
command and receives output(s) from the computer. The means of communication between the user and the
machine is known as the user interface and consists of both hardware and software. There are different types
of interface, which are useful in different situations and for different types of users.
Form based
If the majority of the input to a system is of a standard type, in other words the computer knows what sort of
input to expect, then a typical interface will produce a form on the screen to be filled in. This sort of interface
would be used where an operator is inputting information while asking a customer questions over the
telephone.
The interface:
Prompts the operator to ask all the questions
Makes the operator input the information in the correct order
Ensures that the information is input in the correct format by having specific areas to input the data
Makes the revision of the information much easier.

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1.5 System software
The characteristics of a form based interface are:
It has specified areas for the data. For example, boxes for input of coded material like the date or the
sex of the customer, and areas to be filled in with textual information
It has a cursor which moves to the next box to be filled in, sometimes the box is highlighted to make it
clear to the operator where the data is to be inserted
Some of the boxes are more important than others and the cursor will not move forward until some
data has been entered
It verifies if the input data is sensible for that box before moving on to the next.
Menu based
Menu based interfaces are used in situations where the user is not aware of the options that are available.
Examples of this would be information systems for tourists or users of a particular service. A list of choices
is made available followed by a further set of choices based on the first choice, and so on until the result is
obtained. Imagine a system at a train station in a popular holiday location. The first screen may ask for the
general area of interest (accommodation, trips, shopping, entertainment...); once the choice of accommodation
has been made, the next screen may offer different standards of hotels. The next screen may offer different
price bands, and finally a list of all the available properties that match the previous choices.
Input is often done using a touch screen because of the location of such systems and because the people who
use them are often computer illiterate, meaning that simple systems are the best choice for these scenarios.
Graphical
Graphical interfaces are called GUI (graphical user interface) or WIMP (windows, icons, menus, pointer). The
terms describe what the user sees on the screen. There are many different types, but the user would expect to
be able to view different applications or files on the screen, this is done by putting each into its own bordered
area known as a window. The user will expect to be able to select options by the menus of choices and by
using small icons which represent the different options available. Choices are selected by the user by using
some sort of pointing device to select that choice; typically a mouse would be used.
Natural language
Sometimes referred to as a conversational interface, the computer will ask questions which elicit a response
which gives the user the impression that they are talking to the computer. The trick is that the system asks
questions in a way that only limited answers can be made typically yes or no questions. If the user gives an
invalid response, a message is produced which indicates the user to try again.

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1.5 System software
Command line
Command line or command based interface is one where the user types a series of commands at the keyboard
which tell the computer what their intentions are. The user needs to know what the possible commands are,
and also needs to understand the way files are stored on the system.
The characteristics of a command based interface are:
user must know what the possible commands are?
user must understand the commands and their effects
user needs to understand the way how content is stored in the computer system
Because of the above points there are two very important characteristics about a command based interface.
First, the system is less restricted than the other types of interface. Other interfaces restrict the options that the
user has available to them. This can be particularly important for the system manager because different users
can only be allowed to have access to specific parts of the system. The second characteristic is that command
based interfaces can only be used by computer literate people because you not only have to understand the
commands and their uses but you also need to understand something about how the computer operates,
particular how content is stored.
There are many other points to be made about interfaces, especially the fact that the second part of the
interface consists of the hardware necessary to put the software interface into operation. These points will be
made when the appropriate stage is reached in this course.

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1.5 System software
1.5.2 Utility programs
Utility software is a type of system software designed to help analyze, configure, optimize and maintain the
computer. A single piece of utility software is usually called a utility or a tool.
Utility software should be contrasted with application software, which allows users to do things like creating
text documents, playing games, listening to music or surfing the web. Rather than providing these kinds of
user-oriented or output-oriented functionality, utility software usually focuses on how the computer
infrastructure (including the computer hardware, operating system, application software and data storage)
operates. Due to this focus, utilities are often rather technical and targeted at people with an advanced level of
computer knowledge. There are many examples of utility software but we shall limit ourselves to just a few:
1. The surface of a disk can store so much data that the computer cannot handle it all at once so it needs to be
split up so that data stored on it can be found again. When it is new a disk surface is blank so the computer
“draws lines” on the surface to split it into small areas. The process is called formatting and it is carried out by
a utility program called a disk formatter.
2. When files are to be stored on a disk they need to be managed. This includes arranging for them to be
stored in a certain place, finding files again after they have been stored, moving them around to get them in a
sensible order and deleting them when they are not needed any more. All of these actions are carried out by
utility programs called file handlers.
3. A computer system is made up of lots of different sorts of hardware, each piece of which needs instructions
about how to work. These programs are called hardware drivers.
4. Some files are very large. In most files it is possible to find simple ways of reducing the size of the file
while keeping all its meaning. This can be very important when files are being sent from one computer to
another as the communication is speeded up. The programs that reduce the size of files are called file
compressors.
5. When files are being sent from one computer to another it is possible that they may contain a virus which
will infect the receiving computer. A virus checker (scanner, killer...) is a utility program which keeps a
constant check on files searching for viruses and deletes it if found.

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1.5 System software
1.5.2 Utility programs
6. A disk defragmenter is a utility that reorganizes the files and unused space on a computer’s hard disk so
that the operating system accesses data more quickly and programs run faster. When an operating system
stores data on a disk, it places the data in the first available sector on the disk. It attempts to place data
insectors that are contiguous (next to each other), but this is not always possible. When the contents of a file
are scattered across two or more noncontiguous sectors, the file is fragmented.
Fragmentation slows down disk access and thus the performance of the entire computer. Defragmenting the
disk, or reorganizing it so that the files are stored in contiguous sectors, solves this problem (Figure 8-32).
Operating systems usually include a disk defragmenter. Windows disk defragmenter is available in the System
Tools list.
7. A Disk Check is a free utility that can help you scan your disk drives for errors and fix them. It can also
scan entire disk for bad sectors and try to recover them.
Main Features:
Scan and Fix multiple drives with one click.
Schedule Disk Check on next boot if a drive cannot be locked.
Boot Time Disk check can be performed on multiple drives in a click.
Use of checkdisk makes it highly safe to use.
8. A backup utility allows users to copy, or back up, selected files or an entire hard disk to another storage
medium such as an external hard disk, optical disc, USB flash drive, or tape.
During the backup process, the utility monitors progress and alerts you if it needs additional media, such as
another disc. Many backup programs compress, or shrink the size of, files during the backup process. By
compressing the files, the backup program requires less storage space for the backup files than for the original
files.
Because they are compressed, you usually cannot use backup files in their backed up form. In the event you
need to use a backup file, a restore utility reverses the process and returns backed up files to their original
form. Backup utilities work with a restore utility.

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1.5 System software
1.5.3 Library programs
Library programs are collections of resources used to develop software. These include pre-written code and
subroutines.
Library programs contain code and data that provide services to other programs such as interface (look and
feel), printing, network code and even the graphic engines of computer games. If you have ever wondered
why all Microsoft Office programs have the same look and feel, that is because they are using the same
graphical user interface libraries. For computer games a developer might not have the time and budget to write
a new graphics engine so they often buy graphical libraries to speed up development, this will allow them to
quickly develop a good looking game that runs on the desired hardware.
Most programming languages have a standard set of libraries that can be used, offering code to handle
input/output, graphics and specialist math functions. You can also create your own custom libraries and when
you start to write lots of programs with similar functionality you'll find them very useful. Below is an example
of how you might import libraries into VB.
What is a DLL?
A DLL is a library that contains code and data that can be used by more than one program at the same time.
For example, in Windows operating systems, the Comdlg32 DLL performs common dialog box related
functions. Therefore, each program can use the functionality that is contained in this DLL to implement
an Open dialog box. This helps promote code reuse and efficient memory usage.
By using a DLL, a program can be modularized into separate components. For example, an accounting
program may be sold by module. Each module can be loaded into the main program at run time if that module
is installed. Because the modules are separate, the load time of the program is faster, and a module is only
loaded when that functionality is requested.
Additionally, updates are easier to apply to each module without affecting other parts of the program. For
example, you may have a payroll program, and the tax rates change each year. When these changes are
isolated to a DLL, you can apply an update without needing to build or install the whole program again.

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1.5 System software
1.5.4 Language translators
The final type of system software that you need to know is translator software. This is software that allows
new programs to be written and run on computers, by converting source code (human readable) into machine
code. There are three types that we'll cover in a lot more detail shortly:
Assembler - converts assembly code into machine code
Interpreter - converts 3rd generation languages such as JavaScript into machine code one line at a
time
Compiler - converts 3rd generation languages such as C++ into machine code all at once
Assembler
An assembler translates assembly language into machine code. Assembly language consists of mnemonics
for machine opcodes so assemblers perform a 1:1 ratio translation from mnemonic to a direct instruction. For
example:
LDA #4 converts to 0001001000100100
Conversely, one instruction in a high level language will translate to one or more instructions at machine
level.
Advantages of using an Assembler Disadvantages of using Assembler
 Very fast in translating assembly language to
machine code as 1 to 1 relationship
 Assembly code is often very efficient (and therefore
fast) because it is a low level language
 Assembly code is fairly easy to understand due to the
use of English-like mnemonics
 Assembly language is written for a certain
instruction set and/or processor
 Assembly tends to be optimized for the hardware it's
designed for, meaning it is incompatible with
different hardware
 Lots of assembly code is needed to do relatively
simple tasks, and complex programs require lots of
programming time
Compiler
A Compiler is a computer program that translates code written in a high level language to a lower level
language, object/machine code. The most common reason for translating source code is to create an
executable program (converting from a high level language into machine language).

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1.5 System software
1.5.4 Language translators
Advantages of using a compiler Disadvantages of using a compiler
Source code is not included, therefore
compiled code is more secure than
interpreted code
Tends to produce faster code than
interpreting source code
Produces an executable file, and therefore
the program can be run without need of the
source code
Object code needs to be produced before a
final executable file, this can be a slow
process
The source code must be 100% correct for
the executable file to be produced
Interpreter
An interpreter program executes other programs directly, running through program code and executing it
line-by-line. As it analyses every line, an interpreter is slower than running compiled code but it can take less
time to interpret program code than to compile and then run it — this is very useful when prototyping and
testing code. Interpreters are written for multiple platforms, this means code written once can be run
immediately on different systems without having to recompile for each. Examples of this include flash based
web programs that will run on your PC, MAC, games console and Mobile phone.
Advantages of using an Interpreter Disadvantages of using an Interpreter
Easier to debug(check errors) than a
compiler
Easier to create multi-platform code, as
each different platform would have an
interpreter to run the same code
Useful for prototyping software and testing
basic program logic
Source code is required for the program to
be executed, and this source code can be
read making it insecure
Interpreters are generally slower than
compiled programs due to the per-line
translation method.

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1.6 Security, privacy and data
integrity
1.6.1 Data security
Computer security is a branch of technology known asapplied information security to computers
and networks.
The objective of computer security includes:
Protection of information & property from theft
Corruption, or natural disaster, while allowing the information and property to remain
accessible and productive to its intended users.
Introduction
Information Systems are made of three subclasses, hardware, software and communications with the
purpose to identify and apply information security industry standards, as mechanisms of protection and
prevention, at three levels or layers: Physical, personal and organizational. Essentially, procedures or
policies are implemented to tell people (administrators, users and operators) how to use products to ensure
information security within their organizations.
IT Security
Information security means protecting information and information systems from unauthorized access, use,
disclosure, disruption, modification or destruction. The terms information security, computer security and
information assurance are frequently incorrectly used interchangeably. These fields are interrelated often and
share the common goals of protecting the confidentiality, integrity and availability of information; however,
there are some subtle differences between them.
These differences lie primarily in the approach to the subject, the methodologies used, and the areas of
concentration. Information security is concerned with the confidentiality, integrity and availability of data
regardless of the form the data may take: electronic, print, or other forms. Computer security can focus on
ensuring the availability and correct operation of a computer system without concern for the information
stored or processed by the computer
Confidentiality
Confidentiality is the term used to prevent the disclosure of information to unauthorized
Individuals or systems. For example, a credit card transaction on the Internet requires the credit card number
to be transmitted from the buyer to the merchant and from the Merchant to a transaction processing network.
The system attempts to enforce confidentiality by encrypting the card number during transmission, by limiting
the places where it might appear (in databases, log files, backups, printed receipts, and so on), and by
restricting access to the places where it is stored. If an unauthorized party obtains the card number in any way,
a breach of confidentiality has occurred.

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1.6.1 Data security
Breaches of confidentiality take many forms. Someone looking at your computer screen behind your back
while you have confidential data displayed on it could be a breach of confidentiality. If a laptop computer
containing sensitive information about a company's employees is stolen or sold, it could result in a breach of
confidentiality.
Giving out confidential information over the telephone is a breach of confidentiality if the caller is not
authorized to have the information. Confidentiality is necessary (but not sufficient) for maintaining the
privacy of the people whose personal information a system holds.
Integrity
In information security, integrity means that data cannot be modified without permission. This is not the same
thing as referential integrity in databases. Integrity is violated when an employee accidentally or with
malicious intent deletes important data files, when a computer virus infects a computer, when an employee is
able to modify his own salary in a payroll database, when an unauthorized user vandalizes a web site, when
someone is able to cast a very large number of votes in an online poll, and so on.
There are many ways in which integrity could be violated without malicious intent. In the simplest case, a user
on a system could mis-type someone's address. On a larger scale, if an automated process is not written and
tested correctly, bulk updates to a database could alter data in an incorrect way, leaving the integrity of the
data compromised.
Information security professionals are tasked with finding ways to implement controls that prevent errors of
integrity.
Basic System Security Measures
These Basic System Security Measures apply to all systems. It is a baseline, which all systems must meet.
Note that for most personal workstations, these are the only measures that apply. The requirements are:
1. Authentication and Authorization
Remove or disable accounts upon loss of eligibility: Accounts which are no longer needed
must be disabled in a timely fashion using an automated or documented procedure.
Separate user and administrator accounts: Administrator accounts must not be used for
non-administrative purposes. System administrators must be provisioned with non-
administrator accounts for end-user activities, and a separate administrator account that is
used only for system-administration purposes.
Use unique passwords for administrator accounts: Privileged accounts must use unique
passwords that are not shared among multiple systems. Credentials which are managed
centrally, such as the NetID/password combination, are considered a single account,
regardless of how many systems they provide access to.

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1.6.1 Data security
Throttle repeated unsuccessful login-attempts: A maximum rate for unsuccessful login
attempts must be enforced. Account lockout is not required, but the rate of unsuccessful
logins must be limited.
Enable session timeout: Sessions must be locked or closed after some reasonable period.
Enforce least privilege: Non-administrative accounts must be used whenever possible. User
accounts and server processes must be granted the least-possible level of privilege that allows
them to perform their function.
2. Firewall
Systems must be protected by a firewall that allows only those incoming connections
necessary to fulfill the business needs of that system. Client systems which have no business need to
provide network services must deny all incoming connections. Systems that provide network services
must limit access to those services to the smallest reasonably manageable group of hosts that need to
reach them.
3. Password Protection
All accounts and resources must be protected by passwords which meet the following
requirements, which must be automatically enforced by the system:
Must be at least eight characters long.
Must NOT be dictionary or common slang words in any language, or be relatively easy to
guess.
Must include at least three of the following four characteristics, in any order: upper case
letters, lower case letters, numbers, and special characters, such as “!@#$%^&*”.
Must be changed at least once per year.

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1.6.1 Data security
4. Digital signature
It is basically a way to ensure that an electronic document (e-mail, spreadsheet, text file, etc.)
is authentic. Authentic means that you know who created the document and you know that it has not
been altered in any way since that person created it.
Digital signatures rely on certain types of encryption to ensure authentication. Encryption is the process
of taking all the data that one computer is sending to another and encoding it into a form that only the
other computer will be able to decode. Authentication is the process of verifying that information is
coming from a trusted source. These two processes work hand in hand for digital signatures.
Security measures designed to protect the security of data
Data Backup: Data protection is crucial for protecting your business's continuity. If your only data backup is
on a computer and the hard disk crashes or is damaged by a power surge, your business’s data is gone. And
having paper copies of business data isn't adequate data protection; what if your business premises burns to
the ground or destroyed in a flood? Once again the data you need to carry on your business could be
irretrievably lost.
For adequate data protection, you need to establish a data backup system that follows these three steps:
1) Archive the business data regularly;
2) Create data backups on reliable media;
3) Keep updated data backups in a secure, off-site location.
The basic rule for business data protection is that if losing the data will interfere with doing business, then you
should back it up. You can reinstall software programs if you need to, but recovering the details of transactions
or business correspondence is impossible if those files are lost or damaged beyond repair.
The rest of this article outlines each of the steps listed above so you can establish a data backup system that
will effectively protect your critical business data from disaster.

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1.6.1 Data security
1) Archiving Critical Business Data
Archiving business data is more than a matter of good housekeeping; it could be a matter of your business's
survival.
There are two steps to archiving business data for successful data backup:
1) Identify the critical data that needs to be archived
2) Use a data archiving method on a regular basis.
2) Creating Physical Data Backups
Physical data backups are necessary because of the possibility of computer failure or damage. Even a minor
accident such as spilling a cup of coffee onto your laptop could destroy all your data, if that's the only place
your data resides. You should create physical data backups of your business data at least once a week, or even
more often if your business generates large amounts of new data daily. There are several methods of
transferring your backup files to another media, but some data backup systems are more reliable than others.
3) Off-Site Data Backup
The only businesses that should be keeping their data backups on-site are those with fire-proof, indestructible
safes. Investing in a tape drive or external hard drive and meticulously adhering to a regular data backup
schedule won't help if all your data backup copies are in one place and that place is struck by disaster. You
must store copies of your backups off-site if your business data is to be truly secure.
It is essential to back up the data on servers and other data systems throughout your network. That is obvious.
This section describes a number of ways you can perform backups, including copying data to magnetic tape or
optical disks, or by copying or replicating information to other systems. Before getting started, take note of the
following terminology:
A backup is a copy of online storage information that provides fault protection.
An archive is a historical backup.
An online storage device is a high-performance magnetic disk that stores information that users can
access frequently. Nearline and offline storage devices are slower, secondary storage devices that
provide backup services or archiving services.
Hierarchical file systems move little-used files or large image files from online storage to nearline
storage systems such as optical disk, where they remain available to users.

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1.6.1 Data security
Tape backup systems are the traditional backup medium while optical disk systems provide archiving
and nearline storage requirements
Real-time backups take place at any time and must have a procedure for handling files that are open
during backup. In most cases, the backup system tracks open files and returns to back them up later.
Disk mirroring is a real-time strategy that writes data to two or more disks at the same time. If one
disk fails, the other continues to operate and provide access for users. Server mirroring provides the
same functionality, except that an entire server is duplicated. This strategy allows users to continue
accessing data if one of the servers fails. See "Fault Tolerance and High Availability" for additional
information on these strategies.
Replication copies information to alternate servers on distributed networks to make that information
more readily available to people in other locations. While replication is not necessarily a backup
technique, replicated data on remote servers can be made available to local users should the server
close to them go down.
Remote vaulting is an automatic backup technique that transmits data to alternate sites. The alternate
sites can be more than just warehouses for backups. They may be entire data centers that can be
brought online when the primary data center goes offline in the event of a major disaster.

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1.6.1 Data security
Encryption:
The translation of data into a secret code. Encryption is the most effective way to achieve data security.
To read an encrypted file, you must have access to a secret key or password that enables you to decrypt it.
Unencrypted data is called plain text ; encrypted data is referred to as cipher text.
There are two main types of encryption: asymmetric encryption (also called public-key encryption)
and symmetric encryption.
Symmetric encryption is where the same key is used to encrypt and decrypt the message. This differs
from asymmetric (or public-key) encryption, which uses one key to encrypt a message and another to decrypt
the message.
A cryptographic system that uses two keys -- a public key known to everyone and a private or secret
key known only to the recipient of the message.
When John wants to send a secure message to Jane, he uses Jane's public key toencrypt the message. Jane then
uses her private key to decrypt it.
An important element to the public key system is that the public and private keys are related in such a way
that only the public key can be used to encrypt messages and only the corresponding private key can be used
to decrypt them. Moreover, it is virtually impossible to deduce the private key if you know the public key.
Public-key systems, such as Pretty Good Privacy (PGP), are becoming popular for transmitting information
via the Internet. They are extremely secure and relatively simple to use. The only difficulty with public-key
systems is that you need to know the recipient's public key to encrypt a message for him or her. What's
needed, therefore, is a global registry of public keys, which is one of the promises of the
new LDAP technology.
Public key cryptography was invented in 1976 by Whitfield Diffie and Martin Hellman. For this reason, it is
sometime called Diffie-Hellman encryption. It is also called asymmetric encryption because it uses two keys
instead of one (symmetric encryption).
What is Access Control?
Access Control is any mechanism by which a system grants or revokes the right to access some data, or
perform some action. Normally, a user must first Login to a system, using some Authentication system. Next,
the Access Control mechanism will controls what operations the user may or may not make by comparing
the User ID to an Access Control database.

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1.6.1 Data security
Access Control systems include:
File permissions, such as create, read, edit or delete on a file server.
Program permissions, such as the right to execute a program on an applicationserver.
Data rights, such as the right to retrieve or update information in a database.
Data Integrity vs Data Security
Data is the most important asset to any organization. Therefore, it must be made sure that data is valid and
secure at all times. Data integrity and Data security are two important aspects of making sure that data is
useable by its intended users. Data integrity makes sure that the data is valid. Data security makes sure that
data is protected against loss and unauthorized access.

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1.6.2 Data integrity
What is Data Integrity?
Data Integrity defines a quality of data, which guarantees the data is complete and has a whole structure. Data
integrity is most often talked about with regard to data residing in databases, and referred to as database
integrity as well. Data integrity is preserved only if and when the data is satisfying all the business rules and
other important rules. These rules might be how each piece of data is related to each other, validity of dates,
lineage, etc. According to data architecture principles, functions such as data transformation, data storage,
meta-data storage and lineage storage must guarantee the integrity of data. That means, data integrity should
be maintained during transfer, storage and retrieval.
If data integrity is preserved, the data can be considered consistent and can be given the assurance to be
certified and reconciled. In terms of data integrity in databases (database integrity), in order to guarantee that
integrity is preserved, you have to ensure that the data becomes an accurate reflection of the universe it is
modeled after. In other words, it must make sure that the data stored in the database corresponds exactly to the
real world details it is modeled after. Entity integrity, Referential integrity and Domain integrity are several
popular types of integrity constraints used for preserving data integrity in databases.
What is Data Security?
Data security deals with the prevention of data corruption through the use of controlled access mechanisms.
Data security makes sure that data is accessed by its intended users, thus ensuring the privacy and protection
of personal data. Several technologies are used for ensuring data security. OTFE (on-the-fly-encryption) uses
cryptographic techniques for encrypting data on hard drives. Hardware based security solutions prevent
unauthorized read/write access to data and thus provides stronger protection compared to software based
security solutions. Because software based solutions may prevent data loss or stealing but cannot prevent
intentional corruption (which makes data unrecoverable/unusable) by a hacker.
Hardware based two factor authorization schemes are highly secure because the attacker needs physical access
to the equipment and site. But, the dongles can be stolen and be used by almost anybody else. Backing up data
is also used as a mechanism against loss of data. Data masking is another method used for data security by
which data is obscured. This is done to maintain the security and sensitivity of personal data against
unauthorized access. Data erasure is the method of overwriting of data to ensure that data is not leaked after
its life time has passed.

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What is the difference between Data Integrity and Data Security?
Data integrity and data security are two different aspects that make sure the usability of data is preserved all
the time. Main difference between integrity and security is that integrity deals with the validity of data, while
security deals with protection of data. Backing up, designing suitable user interfaces and error
detection/correction in data are some of the means to preserve integrity, while authentication/authorization,
encryptions and masking are some of the popular means of data security. Suitable control mechanisms can be
used for both security and integrity.
Validation and Verification
When data is input to a computer system it is only valuable data if it is correct. If the data is in error in any
way then no amount of care in the programming will make up for the erroneous data and the results produced
can be expected to be unreliable. There are three types of error that can occur with the data on entry. The first
is that the data, while reasonable, is wrong. If your birthday is written down on a data capture form as 18th
of
November 1983, it will (except in very rare cases) be wrong. It can be typed into the computer with the utmost
care as “181183”, it can be checked by the computer to make sure that is a sensible date, and will then be
accepted as your date of birth despite the fact that it is wrong. There is no reason for the computer to imagine
that it may be wrong, quite simply when you filled out the original form you made a mistake. The second type
of error is when the operator typing in the data hits the wrong key and types in “181193”, or the equivalent. In
this case an error has been made that should be able to be spotted if a suitable check is made on the input.
This type of data checking is called a verification check. The third type of error is when something is typed
in which simply is not sensible. If the computer knows that there are only 12 months in a year then it will
know that “181383” must be wrong because it is not sensible to be born in the thirteenth month. Checks on
the sensibility of the data are called validation checks.
Faulty data:
There is very little that can be done about faulty data except to let the owner of the data check it visually on a
regular basis. The personal information kept on the school administration system about you and your family
may well be printed off at regular intervals so that your parents can check to ensure that the stored information
is still correct.
Verification:
Verification means tallying the input data with the original data to make sure that there have been no
transcription errors. The standard way to do this is to input the data twice to the computer system. The
computer then checks the two sets of data (which should be the same) and if there is a difference between the
two sets of data the computer knows that one of the inputs is wrong. It won’t know which one is wrong but it
can now ask the operator to check that particular input.

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Validation:
The first thing is to clear out a common misinterpretation of validation. Specifically, the use of parity bits to
check data. This is NOT validation. Parity bits and echoing back are techniques that are used to check that
data has been transmitted properly within a computer system (e.g. from the disk drive to the processor),
validation checks are used to check the input of data to the system in the first place.
Validation is a check on DATA INPUT to the system by comparing the data input with a set of rules that the
computer has been told the data must follow. If the data does not match up with the rules then there must be
an error. There are many different types of validation checks that can be used to check input in different
applications:
1. Range check. A mathematics exam is out of 100. A simple validation rule that the computer can apply to
any data that is input is that the mark must be between 0 and 100 inclusive. Consequently, a mark of 101
would be rejected by this check as being outside the acceptable range.
2. Character check. A person’s name will consist of letters of the alphabet and sometimes a hyphen or
apostrophe. This rule can be applied to input of a person’s name so that “dav2d” will immediately be rejected
as unacceptable.
3. Format check. A particular application is set up to accept a national insurance number. Each person has a
unique national insurance number, but they all have the same format of characters, 2 letters followed by 6
digits followed by a single letter. If the computer knows this rule then it knows what the format of a NI
number is and would reject “ABC12345Z” because it is in the wrong format, it breaks the rule.
4. Length check. A NI number has 9 characters, if more or fewer than 9 characters are keyed in then the data
cannot be accurate.
5. Existence check. A bar code is read at a supermarket check-out till. The code is sent to the main computer
which will search for that code on the stock file. As the stock file contains details of all items held in stock, if
it is not there then the item cannot exist, which it obviously does, therefore the code must have been wrongly
read.
6. Check digit. When the code is read on the item at the supermarket, it consists of numbers. One number is
special; it is called the check digit. If the other numbers have some arithmetic done to them using a simple
algorithm the answer should be this special digit. When the code is read at the check-out till, if the arithmetic
does not give the check digit it must have been read wrongly, it is at this point that the beeping sound would
normally be heard if everything is alright.

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Error checking and correcting
When you send data across the internet or even from your USB to a computer, you are sending millions upon
millions of ones and zeros. What would happen if one of them got corrupted? Think of this situation: You are
buying a new game from an online retailer and put £40 into the payment box. You click on send and the
number 40 is sent to your bank stored in a byte: 00101000. Now imagine if the second most significant bit got
corrupted on its way to the bank, and the bank received the following: 01101000. You'd be paying £104 for
that game! Error Checking and Correction stops things like this happening. There are many ways
to detect and correct corrupted data, we are going to learn two.
a) Parity: All data is transmitted as bits (0s and 1s). The Number of 1s in a byte must always be either an odd
number or an even number. If two devices that are communicating decide that there will always be an odd
number of 1s, then if a byte is received that has an even number of 1s, an error must have occurred. E.g. the
byte 01011000 has 3 ones in it. 3 is an odd number, so it fits the rule that it must have an odd number of ones.
When it is sent there is an error in transmission so that the first bit is received as a one. So, the byte received is
11011000. This has 4 ones in it, which is an even number, so there must be an error. The receiving device
would ask for it to be sent again.
Notes:
If two mistakes are made in the same byte they will cancel each other out and the faulty data will be
accepted. This problem can be overcome, and in the same way, a clever way of correcting error mistakes
can be implemented. This method is not part of this course.
Earlier in this course it was said that a byte was the number of bits necessary to hold a character code.
Specifically, an ASCII character uses 8 bits in a byte, giving 256 different characters. This is not true
because one of the bits has to be reserved for a parity bit, the bit that can change to make sure that the
number of ones is always odd. This means that there are 128 different characters possible.
The implication in all the above work is that odd parity is always used. Even parity can equally well be
used, whichever has been agreed between the two devices.
Parity is not only used during data transfer between devices, but even when data is transferred between
different parts of the CPU.

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integrity
b) Check Sum: Data will normally be sent from one place to another as a block of bytes rather than as
individual bytes. The computer can add numbers together without any trouble, so another checking procedure
is to add all the bytes together that are being sent in the block of data. The carry, out of the byte, is not taken
into account, so the answer is an 8 bit number, just like the bytes. This answer is calculated before the data is
sent, and then calculated again when it is received, and if there are no errors in the transmission, the two
answers will match.
Parity Blocks and Parallel Parity
It is an error-checking technique involving the comparison of a transmitted block check character with one
calculated by the receiving device. Parallel parity is based on regular parity. Parallel parity can detect whether
or not there was an error, furthermore it can detect which bit has flipped. This method is implemented on a
block of data which is made of sum words; the parity bit is then added to the columns and rows.
Here’s an example:
1 1 1 0 1 0 1 1
1 1 0 0 0 1 1 0
0 0 1 0 0 1 1 1
0 0 0 0 1 0 1 0

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1.7 Ethics and ownership
1.7.1 Ethics
We may not think about if often, but there are several ethical and legal issues that surround our computer
usage. It is our responsibility to ensure that our computer usage will not negatively affect the other users.
What Are Ethics?
Ethics can be defined as "moral principles that govern a person's or a group's behaviors". Ethical behavior is
not necessarily related to the law. For example, just because something is not against the law doesn't mean it
is okay to do it.
What are Computer Ethics?
Computer ethics are concerned with standards of conduct applying to the use of computers.
Computer ethics can be understood as the branch of applied ethics which studies and analyzes social and
ethical impact of information technology.
The Computer Ethics Institute has published their "Ten Commandments of Computer Ethics" to guide
responsible computer use. They are as follows:
1. Thou shalt not use a computer to harm other people.
2. Thou shalt not interfere with other people's computer work.
3. Thou shalt not snoop around in other people's computer files.
4. Thou shalt not use a computer to steal.
5. Thou shalt not use a computer to bear false witness (aka Lie).
6. Thou shalt not copy or use proprietary software for which you have not paid.
7. Thou shalt not use other people's computer resources without authorization or proper compensation.
8. Thou shalt not appropriate other people's intellectual output.
9. Thou shalt think about the social consequences of the program you are writing or the system you are
designing.
10. Thou shalt always use a computer in ways that ensure consideration and respect for your fellow
humans.

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1.7.1 Ethics
IEEE CS/ACM Code of Ethics and Professional Practice
The Software Engineering Code of Ethics and Professional Practice, produced by the Institution of Electrical
and Electronic Engineers Computer Society (IEEE CS) and the Association for Computing Machinery
(ACM), acts as a professional standard for teaching and practicing software engineering. It specifies ethical
and professional obligations of software engineers and states the standards that standards society at large
expects them to meet and what they should expect of one another. The code also tells the public what they
should expect from software engineers. The code was produced by a multinational task force which
considered input from a variety of sources including industrial, government and military installations and
educational professions. An informative article of about the development of the code, which includes a full
copy of the code itself was published in the October 1999 issue of ACM Computer.
According to the shortened version of the code:
Software engineers shall commit themselves to making the analysis, specification, design, development,
testing and maintenance of software a beneficial and respected profession. In accordance with their
commitment to the health, safety and welfare of the public, software engineers shall adhere to the following
Eight Principles:
Public: Software engineers shall act consistently with the public interest.
Client and Employer: Software engineers shall act in a manner that is in the best interests of their client and
employer, consistent with the public interest.
Product: Software engineers shall ensure that their products and related modifications meet the highest
professional standards possible.
Judgment: Software engineers shall maintain integrity and independence in their professional judgment.
Management: Software engineering managers and leaders shall subscribe to and promote an ethical approach
to the management of software development and maintenance.
Profession: Software engineers shall advance the integrity and reputation of the profession consistent with the
public interest.
Colleagues: Software engineers shall be fair to and supportive of their colleagues.
Self: Software engineers shall participate in lifelong learning regarding the practice of their profession and
shall promote an ethical approach to the practice of the profession.
Professional code of conduct for a computer system developer:

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1.7.1 Ethics
A Code of Conduct is not law, but it is a set of rules that apply when you are in an organization such as your
college. Examples might include "Don't watch pornography at the office". This would be legal at home, but if
you did it at the office, you could be fired. In addition, a code of conduct may contain laws such as "Don't
install pirated software".
The British Computer Society has produced a list of standards for the training and development of
Information Technology workers.
It covers the following issues:
The Public Interest - safeguarding public health; respecting rights of 3rd parties, applying knowledge of
relevant regulations.
Duty to employers and clients - carrying out work according to the requirements, and not abusing employers'
or clients' trust in any way.
Professional duty - uphold the reputation of the profession through good practice, support fellow members in
professional development.
Professional Integrity and Competence - maintain standards of professional skill and practice, accepting
responsibility for work done, avoiding conflicts of interest with clients.
An example of a code of conduct in use in an office is as follows:
Don't play games
Don't watch pornography
Don't gamble
Don't plug your own peripherals into your computer
Don't install software on work machines without permission
(Each of these might be perfectly legal at home, but they might get you fired at work)

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1.7.2 Ownership
Intellectual Property
One of the more controversial areas of computer ethics concerns the intellectual property rights connected
with software ownership. Some people, like Richard Stallman who started the Free Software Foundation,
believe that software ownership should not be allowed at all. He claims that all information should be free,
and all programs should be available for copying, studying and modifying by anyone who wishes to do so
[Stallman, 1993]. Others argue that software companies or programmers would not invest weeks and months
of work and significant funds in the development of software if they could not get the investment back in the
form of license fees or sales [Johnson, 1992]. Today's software industry is a multibillion dollar part of the
economy; and software companies claim to lose billions of dollars per year through illegal copying (“software
piracy”). Many people think that software should be ownable, but “casual copying” of personally owned
programs for one's friends should also be permitted (see [Nissenbaum, 1995]). The software industry claims
that millions of dollars in sales are lost because of such copying. Ownership is a complex matter, since there
are several different aspects of software that can be owned and three different types of ownership: copyrights,
trade secrets, and patents.
One can own the following aspects of a program:
The “source code” which is written by the programmer(s) in a high-level computer language like Java
or C++.
The “object code”, which is a machine-language translation of the source code.
The “algorithm”, which is the sequence of machine commands that the source code and object code
represent.
The “look and feel” of a program, which is the way the program appears on the screen and interfaces
with users.

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1.7.2 Ownership
Consequences of Uses of Computing: Legislation
The way you use data and computers is subject to the law of the country you are living in. Across the world
different countries have different laws, for the exam you only need to learn about the laws that affect the
United Kingdom.
You must be familiar with the following legislation:
Health and Safety (Display Screen Equipment) Regulations 1992
The Health and Safety Act was passed in 1992 and set out to promote excellence in managing health and
safety in the work place. There are strict guidelines on how a desk is set up including provision for monitor
positioning, adjustable chairs etc. Health and Safety is paramount when using computers for prolonged
periods of time. Sitting in front of a computer screen typing and/or using a mouse is not a natural act for a
human being and may result in health problems such as Repetitive Strain Injury (RSI), back and eye issues.
An example of a sensibly laid out work place
The Health and Safety (Display Screen Equipment) Regulations 1992 state that an employer must:

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1.7.2 Ownership
make sure screens are adjustable and have antiglare filters
provide supportive chairs that are adjustable
provide foot supports
provide breaks in computer work routine
pay for eye treatment if necessary
Any employer failing to do this may be subject to a criminal investigation.
Copyright, Design and Patents Act 1988
The Copyright, Design and Patents Act 1988 affects how people can acquire, use and share ideas, software
and media.
Patent
A patent is a form of intellectual property which an individual or organisation owns the right to for a fixed
period of time, allowing them to charge people for the use of it. After that time has expired the idea is in the
public domain. Patents include the design of the light bulb (1841) and the ejector seat (1916).
Computing has seen patents in hardware and more recently in software. There are many people who believe
that software patents are damaging to Computer Science, as they stop innovation and stifle creativity. A
famous case was BT trying to patent the hyperlink. If this had been successful, then every time a hyperlink
was used (every page on the World Wide Web), someone might have had to pay money to BT for the
privilege. Other people see software patents as important in defending the intellectual property of inventors, if
someone creates something new they should be rewarded for it. Other software patents include:
the MP3 and GIF. Countries such as India do not have software patents.

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1.7.2 Ownership
Copyright
Software copyright refers to the law regarding the copying of computer software. Many companies and
individuals write software and sell it for money, these products are copyrighted and you cannot copy the code
or the program without the permission of the maker. This, they believe protects the work of the programmers,
rewarding them for their efforts.
*Copyright symbol Public domain symbol Copy-Left symbol*
Other companies and individuals release software under Free and Open Source software (FOSS) licenses.
These licenses allow users the right to use, study, change, and improve a program's design through the
availability of its source code. Some adherents of FOSS believe it creates better software in the long term, and
others believe that no software should be copyrighted. FOSS licensed products are heavily used in running the
World Wide Web and in the creation of popular websites such as Facebook. Open Source licenses generally
mean that if you create software that makes changes to open source code, and choose to release it, you must
release your new code under the same Open Source license, this is called Copy-Left. Some free software is in
the public domain, meaning that you can use it for whatever purpose you wish, if you make a software product
involving changes to public domain sources code, you don't have to release your code into the public domain.
Copyright in most works lasts until 70 years after the death of the creator if known, otherwise 70 years after
the work was created or published (fifty years for computer-generated works).
In summary the act specifies that users are not allowed to:
use copyright material without permission
use patented design without permission
edit programs without permission
copy or distribute software without permission

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1.7.2 Ownership
Computer Misuse Act 1990
The Computer Misuse Act 1990 deals with people who crack computer programs or systems. Crimes might
include removing the Copyright protective measures from a commercial software product, breaking into a
school database to change grades, hacking into a companies' website and stealing customer credit card details,
creating viruses and trojans, and so on. It was recognized in the late 1980s that the increase in business and
home use of computers required legislation in order to protect against their exploitation. To this end, in 1990
the Computer Misuse Act was established.
Under the act, three new offences were created:
It prohibits:
1) Unauthorized access to computer material
a. There must be proof that the perpetrator accessed the data, and that he was unauthorized and
wasn’t aware of the fact that he was unauthorized.
2) Unauthorized access with intent to commit or facilitate commission of further offences
a. To prove ulterior intent, it must be shown that they wished to use the information in order to
commit a further offence.
3) Unauthorized modification of computer material
a. Unauthorized modification also includes deliberate introduction of a virus onto a computer
system.

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1.7.2 Ownership
"Obtaining access" means; "Causing the computer to perform any action the results in it": Copying/moving
data, Erasing/altering data, using a program; or causing the computer to output programs or data.
A difficulty with computer crime is that it can cross physical and national borders; the Computer Misuse Act
recognizes this fact and gives British Courts the jurisdiction where a "significant link" with Britain can be
demonstrated in instances of computer-related crime. America has its own Computer Fraud and Abuse Act.
Data Protection Act 1998
The Data Protection Act 1998 controls the way that companies, organizations and individuals handle personal
data.
It states that:
1. Data may only be used for the specific purposes for which it was collected.
2. Data must not be disclosed to other parties without the consent of the individual whom it is about,
unless there is legislation or other overriding legitimate reason to share the information (for example,
the prevention or detection of crime). It is an offence for Other Parties to obtain this personal data
without authorization.
3. Individuals have a right of access to the information held about them, subject to certain exceptions
(for example, information held for the prevention or detection of crime).
4. Personal information may be kept for no longer than is necessary and must be kept up to date.
5. Personal information may not be sent outside the European Economic Area unless the individual
whom it is about has consented or adequate protection is in place, for example by the use of a
prescribed form of contract to govern the transmission of the data.
6. Subject to some exceptions for organizations that only do very simple processing, and for domestic
use, all entities that process personal information must register with the Information Commissioner's
Office.
7. The departments of a company that are holding personal information are required to have adequate
security measures in place. Those include technical measures (such as firewalls) and organisational
measures (such as staff training)
8. Subjects have the right to have factually incorrect information corrected (note: this does not extend to
matters of opinion)

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1.7.2 Ownership
Regulation of Investigatory Powers Act 2000
The Regulation of Investigatory Powers Act was passed in 2000, and introduces the power to intercept
communications with the aim of taking into account the growth of the Internet. It regulates the manner in
which certain public bodies may conduct surveillance and access a person's electronic communications.
Supporters of the act claimed this was an excuse to introduce new measures, some of these included being
able to force someone to reveal a cryptographic key for their data, with failure to do so resulting in up to 2
years imprisonment. As we have seen in packet switching, data can be read in transit between hosts. However,
the act goes further than allowing this:
enables certain public bodies to demand that an ISP provide access to a customer's communications in
secret;
enables mass surveillance of communications in transit;
enables certain public bodies to demand ISPs fit equipment to facilitate surveillance;
enables certain public bodies to demand that someone hand over keys to protected information;
allows certain public bodies to monitor people's internet activities;
prevents the existence of interception warrants and any data collected with them from being revealed
in court.
Software License
A software license is a legally binding agreement that specifies the terms of use for an application and defines
the rights of the software producer and of the end-user.
All software must be legally licensed before it may be installed. Proof of purchase (purchase orders, receipts,
invoices or similar documentation are acceptable) must be maintained by individuals or departments.
Software licensing can be a confusing subject. There are different types of licenses and licensing contracts,
and different vendors may use different terms to describe their licenses. Here are some key terms to help you
navigate through these murky waters.

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1.7.2 Ownership
Software License Types
Individual (Single-user): This license type allows the program to be installed and used on one CPU which is
not accessed by other users over a network. The software will only be used on a single computer, and other
users will not be able to access or run the software while connected to your computer.
Types of individual licenses are:
1. Perpetual license: allows the customer to install and use the software indefinitely. Technical
support is included for a limited term, usually 90 days.
2. Subscription license: Allows the user to use the software for a specified time period. This license
usually includes technical support and access to upgrades and patches released during the term of
the subscription. At the end of the term the user has several options: (1) renew the subscription; or
(2) purchase a perpetual license at a discounted cost; or (3) remove the software from the
computer.
3. Freeware license: This license type is offered as freeware by the author and does not require
paying any fee for use.
4. Shareware license: This is a license to use software for a trial period and then, if you continue to
use the software, you must pay a shareware fee or cease using the software.
Special Channel Licenses
1. OEM (original equipment manufacturer): These licenses cover software for stand-alone PC's and
notebooks and MUST stay bundled with the computer system and NOT distributed as a separate (or
stand-alone) product. This software will be identified or labeled "For Distribution Only With New
Computer Hardware."
2. Educational or Academic Software: Software marked for distribution to educational institutions and
students at reduced prices. This software is usually labeled that it is an academic product and for use
only by academic or educational institutions.
3. Not for Resale (NFR) Software License: Specific and restricted licenses that are made available by
software vendors directly to the distribution channel and are typically marked NFR with explicit
conditions that it is NOT FOR RESALE. The NFR software is not licensed for normal commercial
distribution.
4. Concurrent Use: This license type requires that you purchase licenses for the maximum number of
people who will be running the software simultaneously.

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1.7.2 Ownership
Freeware. In general, freeware is available at no cost and with no restrictions. Freeware tends to be simple
software designed to perform one or two tasks.
Shareware. Shareware is free to try out. You usually have to pay if you want to continue using it. Some
shareware relies on the honesty of users to pay up when they should.
Open source business software. Open source software can be freely adapted by anyone with the knowledge
and inclination to do so. The open source system has created many useful pieces of software that are the
product of loose collaboration between many people, all over the world.
Freemium software. This is a relatively new model for software. It mainly applies to online software that you
access over the internet. With freemium software certain basic features are free, but if you need more
advanced functions, you’ll have to pay for them.
Types of licenses
Proprietary license
Most software licenses are "proprietary" licenses, meaning the software publisher grants a license to use one
or more copies of software, but that ownership of those copies remains with the software publisher. The user
must accept the license before they are permitted to use the software.
GNU General Public License
These are agreements under which much "open source" software is licensed. End users may do things like
change the source code, but any refinements of the software must also be made available under a GNU GPL
license. Often referred to as "free, copyleft" licenses, the software may or may not be distributed for a fee -
"free" refers to the ability of users to change and distribute modifications of the software, not to cost. See the
GNU General Public License web page for more information.
End User License Agreement (EULA)
Also called "clickwraps" or "shrink wraps," EULAS indicate the terms under which the end-user may use the
software. Agreements with organizations or companies often take the form of contracts between the
organization and the software publisher or vendor, and specify the terms of use for all users from the
organization, superseding any EULAs which may come with the software.
Workstation licenses
These are licenses that permit the installation of an application on a single computer. You may not install the
software on more than one machine unless you purchase a license for each additional machine. Most
workstation license agreements allow you to make a single backup copy of the software as long as that backup

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1.7.2 Ownership
copy is used only to restore the software onto the same machine, or a separate machine if the software is
removed from the original computer.
Concurrent use license
These are licenses that permit you to install the software onto multiple machines as long as the number of
computers using the software at the same time does not exceed the number of licenses which you have
purchased. Concurrent use licenses are usually used in conjunction with "license manager" software that
prevents the number of licenses from being exceeded. At UNCG, ITS uses KeyServer software that monitors
and controls the use of concurrent use licensed software.
Site licenses
A site license permits the use of software on any computer at a specified site. Unlimited site licenses allow the
installation of software on any number of computers as long as those computers are located at the specified
site. Some site licenses permit the installation on computers owned by a particular entity (such as a university)
regardless of the physical location. Some vendors refer to their licenses as site licenses but restrict the number
of computers on which the software may be installed. The only way to know for sure is to read the license
specifics.
Perpetual licenses
These are licenses without expiration dates, which permit use of the software indefinitely, without requiring a
recurring fee for continued use. Most software that individuals buy for use on their home computers are
perpetual licenses.
Non-perpetual licenses
These are licenses that "lease" the software for use for a specified period of time, usually annually or
sometimes bi-annually. Users are required to remove the software from their computer if they cease paying
the license fee.
License with Maintenance
Some license agreements allow the user to purchase "maintenance" or "software assurance" along with the
original license fee, which entitles the user to receive new versions of the software for one to two years until
the maintenance agreement expires.

As Level Computer Science Book -1

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