Lecture 4b - Computer Elements_ Processing unit & memory.pdf

Computer Processing
unit
By Fidea F. Chambo

The System Unit
A computer system unit, also known as a computer tower, is
the main box-like structure of a computer that contains the
essential components for the computer to work
Many people erroneously refer to this as the CPU.
The computer system unit is the housing that contains the
main components of the computer.
System units come in two basic varieties,
the tower version,
or a desktop version,

Inside the system unit, you'll find the CPU (central
processing unit), the main circuit board (known as the
motherboard), RAM (random access memory), and other
components.

Components inside the system Unit

Main Components of a PC System
Unit
The main components inside the computer system
unit are such as:
– Central Processing Unit (CPU),
– Memory Unity
– Storage Unit - Hard Disk Drive/SSD,
– Motherboard
– Databus
– Power supply
– And others…

The central processing unit (CPU)
Central processing unit (CPU): The "brain" of the
computer that executes functions, processes, and digital
instructions. Sometimes it is known as Microprocessor
or Processor.
The CPU is the hardware component responsible for all
operations performed in the computer system, that’s
why most computer users call it the brain of the
computer, which is fixed on the motherboard through a
slot.
This is where all calculations
and every instruction take place.

Processors are typically
found on a single silicon
chip and are often part of
the Intel Pentium family.
More pins indicate
greater processing
capability.

History of CPU
Since 1823, when Baron discovered silicon, which is still
the primary component used in manufacturing CPUs today,
the history of the CPU has experienced numerous
significant turning points.
The first transistor was in December 1947. in 1958, the first
working integrated circuit was built.
The Intel 4004 was the company’s first microprocessor,
which it unveiled in 1971.
Intel released its 8008 CPU in 1972, Intel 8086 in 1976,
and Intel 8088 in June 1979,
The Motorola 68000, a 16/32-bit processor, was also
released in 1979.
The Sun also unveiled the SPARC CPU in 1987.

AMD unveiled the AM386 CPU series in March 1991.
In January 1999, Intel introduced the Celeron 366 MHZ and
400 MHz processors.
AMD back in April 2005 with its first dual-core processor.
Intel also introduced the Core 2 Dual processor in 2006.
Intel released the first Core i5 desktop processor with four
cores in September 2009.
In January 2010, Intel released other processors like the
Core 2 Quad processor Q9500, the first Core i3 and i5
mobile processors, and the first Core i3 and i5 desktop
processors.
In June 2017, Intel released Core i9 desktop processor, and
Intel introduced its first Core i9 mobile processor In April
2018.

Functions of CPU
The key functions of a CPU are as follows −
– The CPU performs all arithmetic and logic operations.
– It executes all instructions provided by a program and
runs the operating system as well as application software.
– It constantly receives input from the user and directs the
Input and output units to respond to the instructions
communicated to the processor.
– It contains registers, which are small storage locations
within the CPU used for holding intermediate results and
instructions.
– The CPU conducts all data processing operations by
fetching instructions from memory, decoding them, and
then executing them.
– Finally, it processes the data and produces output, which
may be displayed on the screen.

Processor vs Core i Processor
A CPU core is a single processing unit within the
CPU.
A core is a small CPU or processor built into a big
CPU or CPU socket. It can independently perform
or process all computational tasks. A core can
execute only one program instruction at a time
A CPU can have multiple cores, which allows it to
run multiple tasks simultaneously. The more cores a
CPU has, the more independent tasks the processor
can run concurrently

Multi-core Processor
Traditional processors, such as the Pentium processor,
had only one core. In contrast, modern processors are
multi-core.
A multi-core processor is an integrated circuit that has
two or more processor cores. These cores work together
to enhance performance and reduce power
consumption.
Essentially, a multi-core processor is like a package
containing several processors, referred to as cores,
within it.
These processors can execute multiple instructions
simultaneously, depending on the number of cores.

The Core "i" name processors, such as i5 and i7,
serve as a way to categorize and differentiate
processors within a specific generation but not refer
to the number of cores inside the processor.
For instance, a Core i7 processor typically has
between 6 to 20 cores, while a Core i5 processor
usually has between 4 to 14 cores.
The following is the Intel Core Processor Family
and possible number of cores

Intel® Core Processor
Family
Intel® Core i9 Processors: Delivering up to 24
cores
Intel® Core i7 Processors: This CPU packs the
power of up to 20 cores.
Intel® Core i5 Processors: PCs with up to 14
cores
Intel® Core i3 Processors: processors deliver
outstanding performance for everyday tasks.
Intel® Core Processors: For casual gaming,
multitasking,

Processor Speed
CPU speed, also known as clock speed, refers to the
number of cycles a CPU can execute in one second. It is
measured in hertz (Hz).
Clock speed represents how many times per second a
circuit operates, or the speed at which a microprocessor
can execute instructions.
Hertz (Hz) measures the number of electronic pulses
generated by the clock per second; which relates to the
frequency at which the CPU operates or the number of
cycles the processor executes each second.
Understanding the type and speed of your computer's
processor is important.

 CPU usually expressed in megahertz (MHz) or
gigahertz (GHz), determines how fast your computer
will run.
 The faster the processor in a computer, the more
quickly the computer will perform operations
 For example, a CPU with a clock speed of 3.0 GHz
can process 3 billion cycles per second, where 3.0
MHz can execute 3 million cycles per second
Higher processor speeds, combined with the number
of cores, enhance computing capabilities for various
user needs such as gaming or business tasks.

Types of CPU
Single Core CPU: These CPUs only have a single
core that performs different operations. The oldest
type of CPU was used in the 1970s.
Dual-Core CPU: Dual-Core CPUs contain a single
Integrated Circuit with two cores. Dual-core CPUs
can work faster than single-core processors.
Quad-Core CPU: A quad-core processor contains a
chip with four independent cores. These cores read
and execute various instructions provided by the
CPU.

What Makes a Good CPU
Speed?
When considering what’s a good CPU speed, it’s important
to understand that higher numbers generally mean better
performance. Here are some key points to consider:
– For general use: A CPU speed of 1.6 GHz to 2.5 GHz is
typically sufficient for tasks like web browsing, word
processing, and basic multimedia.
– For gaming: Generally, a speed of 3.5 GHz to 4.0 GHz is
considered good for gaming.
– For professional use: Content creators, data analysts, and
other professionals might need speeds of 4.0 GHz and above,
depending on their specific applications.

Choosing the Right Processor for Your Needs
When selecting a CPU, consider your use case:
For everyday computing: Look for multi-core
processors with speeds around 2.5 GHz to 3.5 GHz,
such as Intel Core i5.
For gaming: Aim for processors with speeds of 3.5
GHz to 4.0 GHz or higher, like Intel Core i7.
For professional use: Consider high-end processors
with speeds of 4.0 GHz and above, such as Intel
Core i9
Remember, the best processor for you balances
speed, core count, and price according to your needs.

Components of CPU
The processor itself is made up of components such as the
arithmetic logic unit (ALU) and the control unit (CU).
Additionally, the processor has internal memory called a
register that stores a small number (usually less than 100) that is
currently being processed. This register works very closely with
the main memory location called RAM, which retains active
programs and data.
The components of the CPU are:
– Control Unit (CU)
– ALU (Arithmetic Logic Unit)
– Registers and
– Memory Unit

1. Control Unit (CU)
CU is the part of the CPU that supervises the general
operations of the computer. It controls the operations of all
parts of the computer.
It controls the data flow between the CPU, memory, and
other peripherals.
A CPU executes instructions by fetching them from
memory, decodes them, and then executes them. Also, the
CPU reads and writes data to and from the memory system
and transfers data to and from the I/O devices.
A major role of a control unit is fetching instructions from
the main memory, decoding them, executing them, and
transferring data to and from the I/O devices.

Functions of Control Unit
Instruction Fetch − A CU fetches instructions from
RAM (Random Access Memory).
Instruction Decoding − It decodes the fetched
instructions to operate.
Instruction Execution − A CU sends control
signals to perform arithmetic and logical operations.
Control Flow Management − It controls the flow
of instructions from software.
Exception Handling − A control unit effectively
manages exceptions like hardware failures.

2. Arithmetic Logic Unit (ALU)
Arithmetic logic unit (ALU) is a circuit embedded
within a computer’s central processing unit (CPU),
which performs mathematical and logical operations
using electrical transistors that convey signals in 0s
and 1s.
As the name implies, the Arithmetic and Logical
Unit (or ALU) performs arithmetic and logical
functions. The arithmetic functions are addition,
subtraction, multiplication division, and
comparisons, whereas the logical functions mainly
include selecting, comparing, and merging the data.

Functions of ALU
Arithmetic Operations: The ALU can perform
basic arithmetic operations. It executes arithmetic
operations such as addition, subtraction, and
multiplication.
Logic operations: The ALU can also perform
logical operations like AND, OR, NOT, XOR, and
bit-shifting

3. Memory Unit
Memory refers to the temporary internal storage
areas within a computer where data that need to be
processed and instructions required for processing
are stored.
Memory is used to store the information (programs
and data) that the computer is currently using. It is
sometimes called main or primary memory.
The memory unit supplies the data to other units of
the computer whenever it is required to do so.
There are two types of memory in the computer,
which are primary memory and secondary memory.

Primary Memory
Primary storage or memory is also known as the main
memory, which is the part of the computer that stores
current data, programs, and instructions.
Primary memory is a segment of computer memory that
can be accessed directly by the processor. In a hierarchy
of memory, primary memory has access time less than
secondary memory. Generally, primary memory has a
storage capacity lesser than secondary memory.
In order to enhance the efficiency of the system,
memory is organized in such a way that access time for
the ready process is minimized.

The following approach is followed to minimize
access time for the ready process.
All programs, files, and data are stored in secondary
storage that is larger,
to execute any process operating system loads the
process in primary memory which is smaller and can
be accessed directly by the CPU and hence has
greater access time..
Since only those processes are loaded in primary
memory which is ready to be executed, the CPU can
access those processes efficiently and this optimizes
the performance of the system.

Classification of Primary Memory
Primary memory can be broadly classified into two
parts:
1. Random Access Memory (RAM)
2. Read-Only Memory (ROM)

RAM (Random Access
Memory)
Random Access Memory (RAM) is
also known as an internal storage unit or main memory,
it is the main ‘working’ memory used by the computer
which holds only those data and instructions on which
the computer is currently working.
RAM is volatile, which means RAM store data
temporarily and data stored in it is lost when we switch
off the computer or if there is a power failure.
The contents of RAM are necessary for the computer to
process data. A computer cannot run without
primary memory

The RAM within your computer is where the
operating system is loaded to when you switch on
your computer. Any process in the system which
needs to be executed is loaded in RAM which is
processed by the CPU as per Instructions in the
program.
The units which are used to measure
computer memory are bytes.
RAM has limited capacity, currently ,
PCs typically have 1GB to 32GB of RAM.
While RAM is used for short-term storage, the more
things you open on your computer, the more GB of
RAM you need.

How much RAM do you need?
The size of RAM affects speed, power and
capability of a computer system. As a rule of thumb,
the more RAM you have installed in your computer
the better.
Generally, it is recommended to have
– 4-8GB of RAM for casual computer usage and internet
browsing,
– 8-16GB for spreadsheets and other office programs, and
– at least 32GB for gamers and multimedia creators.
How you use your computer influences how much
RAM you need, so use this as a guideline.

ROM (Read Only Memory )
Read-Only Memory (ROM) is a type of primary
memory from which information can only be read.
ROM is a special type of memory chip which holds
software which can be read but not written to it.
ROM can be directly accessed by the Central
Processing Unit. But, the data and instructions
stored in ROM are retained even when the computer
is switched off.
This type of memory is non-volatile. Means, the
information is stored permanently in such memories
during manufacture.

ROM is typically used to store programs and data
that are required to start up (boot) a computer
system. This operation is referred to as bootstrap.
Another use of ROM, is to store operating systems
subprograms for carrying out I/O and other
activities.
Any data which need not be altered are stored in
ROM. ROM includes those programs which run on
booting of the system (known as a bootstrap
program that initializes OS) along with data like
algorithm required by OS. Anything stored in ROM
cannot be altered or changed.

ROM chips are not only used in the computer
but also in other electronic items like washing
machine and microwave oven. Also, network
cards and video cards contain ROM chips.
A good example is the ROM-BIOS chip,
which contains read-only software for Basic
I/O devices.

Different between RAM and ROM
RAM ROM
RAM is a data storage that
can be accessed randomly at
any time, in any order and
from any physical location.,
ROM Stores instructions that
are necessary for booting up
and to make the computer
operate when it is switched off.
RAM chip is used in the
normal operations of a
computer once the OS is
loaded.
A ROM chip is used primarily
in the startup process of a
computer,
RAM is volatile i.e. its
contents are lost when the
device is powered off.
ROM is non-volatile i.e. its
contents are retained even
when the device is powered off.

4. Registers
A CPU register is a small piece of computer
memory that stores and manipulates data while
instructions are executed. It has small amount of
memory associated with the CPU, which it uses to
perform the operations.
A register may hold an instruction, a storage
address, or any kind of data (such as a bit sequence
or individual characters).
It is also the cache, which serves as high-speed
memory where instructions can be copied to and
retrieved.

The register size of a particular processor allows us
to classify the processor. Depending on the
processor, a register may typically store 8, 16, 32 or
64 bits.
Processors with a register size of n-bits are called n-
bit processors, so that processors with 8-bit registers
are called 8-bit processors, similarly there are 16-
bit, 32-bit and 64-bit processors etc.
An n-bit processor is said to have an n-bit word size
so a 32-bit processor has a 32-bit word size.
The greater the number of bits the more powerful
the processor is, since it will be able to process a
larger unit of information in a single operation.

32-bit vs 64-bit
You’ve probably heard when you download a piece
of software, the term 32-bit and 64-bit.
This term is used for processor, Operating System,
install a game, computer driver etc.
There are two type processors exist in computing
i.e. 32-bit and 64-bit.
The term x86 is used for architecture of the CPUs
that means x86 stands for 32 bits and it refers to the
family of processors (80386 and 80486). The
term x64 stands for 64 bits processors.

Data Bus
DataBus is the physical connection that makes it
possible to transfer data from one location in the
computer system to another. It composed of a set of
communication lines or wires
DataBus is the channel or path that lets the parts of a
computer communicate with each other. Data travels
from one part of the computer to another through a
bus. This is used to transfer information between all
system components.
A data bus is utilized to transport data from the
memory to the registers and from the registers to the

An alternative method of classifying a processor is
to use the width of the data bus. This means that the
CPU can transfer n-bits to another device in a single
operation.
Databuss width is measured by using bits
The data bus width is very important in a computer
system, since it determines the amount of
information that can be transferred to or from the
CPU, in a single operation.
This means, for example, if the data bus width is 16-
bits, then would have to transfer two 16-bit items to
the CPU to fill a 32-bit register.

Motherboard
Motherboard is the computer's main circuit board
that connects all components of a microcomputer. It
is also known as System board.
A motherboard is often referred to as the
“backbone” or “spine” of a computer.
The CPU is normally housed on system board along
with all the other electronic components that has
connectors for attaching devices to the bus.
It allocates power and allows communication
between the CPU (central processing unit), RAM
(random-access memory), and all other computer

There are multiple types of
motherboards, designed to
fit different types and sizes
of computers.
Each type is designed to
work with specific types of
processors and memory, so
they don't work with every
processor and type of
memory.
However, hard drives are
mostly universal and work
with most motherboards,
regardless of the type or
brand.

Secondary Memory
Secondary storage, is a computer system's long-term
storage component that stores data that's not accessed
frequently.
These are also known as Long term storage or
Permanent Storage, and external memory or backup
memory or auxiliary storage,
They are non-volatile storage such that data is
permanently stored even if power is switched off and
can be used to store, back up, and archive data.
It is slower than main memory. Contents of secondary
memories are first transferred to main memory, and
then CPU can access it. CPU does not access these
memories directly instead they are accessed via input-
output routines.

Secondary memory is used for different purposes,
the main purposes of using secondary memory are:
Permanent storage: As we know primary memory
stores data only when the power supply is on. So we
need a secondary memory to store data permanently
even if the power supply is off.
Large Storage: Secondary memory provides large
storage space so that we can store large data like
videos, images, audio, files, etc permanently.
Portable: Some secondary devices are removable.
So, we can easily store or transfer data from one
computer or device to another.

Three main types of secondary storage
Magnetic storage: Uses magnetized fields to store data in
binary form on a metal disk or magnetic tape. Hard disk drives
(HDDs) and magnetic tape are examples of magnetic storage.
Solid state storage: Uses silicon microchips with transistors to
store data. Solid-state drives (SSDs) and USB memory sticks are
examples of solid-state storage. Faster read and write speeds
than HDDs and optical storage devices, and consume less power
and generate less heat. USB flash drives are compact and
portable, while SSDs are more commonly installed internally
within a computer.
Optical storage: Uses microscopic light reflected off a metal or
plastic disk to store data. CDs, DVDs, and Blu-ray discs are
examples of optical storage. Portable, durable, and low-cost.

Magnetic storage devices
Magnetic storage devices are storage devices that use
mechanical and binary technology to record information. This is
because they use a moving part to mark and read information on
a magnetic surface.
Magnetic storage devices use magnetization process to write,
rewrite and access data. Data gets saved here in binary form.
These devices store data in the form of tiny, magnetized dots.
The dots are created, read and erased using magnetic fields
created by very tiny electromagnets.
Magnetic storage is one of the most affordable ways to
store large amounts of data.

Magnetic storage are of two categories Magnetic tape and
Magnetic Discs
In the magnetic tape the dots are arranged along the length of
a long plastic strip which has been coated with a magnetizable
layer (audio and video tapes use a similar technology).
In the magnetic discs the dots are arranged in circles on the
surface of a plastic, metal or glass disc that has a magnetizable
coating(e.g. floppy disc or hard-drive), .
Some of the most common magnetic storage devices include:
– Magnetic Tapes.
– Hard Disk Drives (HDDs)
– Floppy Disks.

1. Magnetic Tape
Magnetic tape storage is a method of storing digital
data on a thin plastic strip with a magnetic
coating. It contains thin plastic ribbon coated with magnetic
oxide.
It was a primary storage medium for early
computers and is still used today for data backup
and archiving
Magnetic tape is made up of a thin, magnetizable
coating on a long, narrow strip of plastic film.
Devices that record and play audio and video using
magnetic tape are tape recorders and videotape
recorders.
A device that stores computer data
on magnetic tape is known as
a tape drive.

In magnetic tape only one side of the ribbon is used for storing
data.
It uses 'serial access' to find a piece of data. This
means that to find a specific piece of data, the tape
reader has to start at the beginning of the tape
and continue fast forwarding until it gets
to the piece of data that needed.
Serial access makes it fairly slow to find and retrieve data. Data
read/write speed is slower because of sequential access.
However, magnetic tape is excellent for archiving data i.e. data
not likely to be needed instantly.
Tape data storage is used more for system
backup, data archive and data exchange. The
low cost of tape has kept it viable for long-term
storage and archive

Advantages and Disadvantages of Magnetic
Tape
Advantages :
These are inexpensive, i.e., low cost memories.
It provides backup or archival storage.
It is a reusable memory.
It is compact and easy to store on racks.
Disadvantages :
Sequential access, means it does not allow access randomly or
directly.
It requires caring to store, i.e., vulnerable humidity, dust free, and
suitable environment.
It’s stored data cannot be easily updated or modified, i.e., difficult to
make updates on data.

2. Hard Disk Drive (HDD)
Hard Disk Drives (HDDs) are the most common magnetic
storage devices found in computers and data centers. Hard-
drives have a very large storage capacity (up to 1TB).
An HDD is composed of several circular
disks, called platters, which store data on their
magnetic surfaces. These platters spin at high
speeds, allowing the read-write head to access the
stored data.
The surface of a disk is divided into tracks and each track is
divided into sectors (blocks).
Disk storage is the most popular form of secondary storage. It is
more versatile than tape storage.

Hard-drives are random access devices and data access
speeds are very fast.
It is faster to access, as information can be accessed (direct
access) quickly, independently of its position on the disk.
Its disadvantage is that it is more expensive than tape
storage.
It is measured in a Byte, they can be used to store vast
amounts of data. For example, a modern 2TB HDD can
store millions of text documents, hundreds of hours of high-
definition videos, or thousands of high-resolution images.
This is the main, large data storage area within your
computer.

Internal Hard Disk
Internal Hard disks are the main data storage area within
your computer and are used to store your operating system,
your application programs (i.e. your word processor, games
etc) and your data.
They are much faster than CD-ROMs and floppy disks and
can also hold much more data.
Hard disks are installed within the system unit of
your computer.

External hard disks
External Hard Drives are similar to internal HDDs,
external hard drives are portable devices that house an
HDD in an external casing, allowing users to store and
transfer data between multiple computers with ease.
They also offer varying capacities, from gigabytes to
terabytes. Some external hard disks will plug into the
USB port (connector) located at the back of your
computer.
Other external hard disks require the installation of a
special card within your computer which allows the
connection of the external hard disk to the computer
unit.
Normally slower than internal disks, but more

3. Floppy disk
A floppy disk is a flexible removable storage device also known as a
diskette. It is a type of disk storage composed of a thin and flexible
disk of a magnetic storage medium in a square or nearly square plastic
enclosure lined with a fabric that removes dust particles from the
spinning disk.
It has a flexible plastic disk covered with a thin layer of a magnetic
substance, onto which digital data can be recorded and stored.
It is the oldest portable storage devices that was commonly used to
store computer files from the 1970s to the 1990s
but are not used that much now due to their
limited storage capacity.
They are very slow compared to hard disks, and
hold relatively small amounts of data (1.44
Mbytes).

Comparison
Type
Storage
Capacity
Access
Method
Primary Use
Hard Disk
Drives
GB to TB
Random
Access
Data Storage in
Computers and
Data Centers
Floppy
Disks
KB to MB
Random
Access
Portable Data
Storage (Historical)
Magnetic
Tapes
GB to TB
Sequential
Access
Backup and
Archivi

Solid state storage (SSD)
STORAGE
Solid-state drive (SSD) is a solid-state storage device that uses
integrated circuit assemblies as memory to store data.
SSD stores the data on flash memory chips making it faster and
more efficient than a traditional hard disk drive (HDD)
There are no moving mechanical components in SSD. This
makes them different from conventional electromechanical
drives such as Hard Disk Drives (HDDs) or floppy disks, which
contain movable read/write
heads and spinning disks.
That's why they are called
solid-state drives

SSDs have lower latency compared to electromechanical
devices they are more resistant to physical shock, run
silently, and have quicker access time. As a result, SSDs
offer advantages such as reduced boot times, quicker file
transfers, and advanced system overall performance.
SSDs may be constructed from random-access memory
(RAM) for applications requiring fast access but not
necessarily data persistence after power loss.
Batteries can be employed as integrated power sources in
such devices to retain data for a certain amount of time after
external power is lost.

Advantages of SSD
Faster Read/Write Speeds: SSDs offer significantly faster read and
write speeds than traditional hard disk drives (HDDs), which use
spinning disks and mechanical read/write heads.
Lower Power Consumption: SSDs consume less power than HDDs,
making them ideal for use in laptops, tablets, and other mobile devices
that rely on battery power.
No Moving Parts: SSDs have no moving parts. This makes them
more resistant to shock and vibration, and less prone to mechanical
failure.
Higher Reliability: Because SSDs have no moving parts, they are
generally more reliable than HDDs, SSDs also have a lower rate of
data loss due to read/write errors.
Lower Noise and Heat Output: SSDs generate less noise and heat
than HDDs,

Disadvantages of SSD
Cost: SSDs are more expensive than regular hard drives.
Limited Lifespan: Each memory cell in an SSD has a
limited number of write cycles before it degrades.
Storage choices: Because of the expense, SSDs are often
sold in smaller sizes.
Performance: SSDs’ performance degrades over time due
to write cycle limitations.

Difference Between SSD and HDD
Parameter HDD SSD
Long term
storage
HDDs are more reliable
for long-term storage.
SSDs are comparatively less reliable for long-
term storage due to data leaks that can occur if
kept unpowered for more than a year.
Access speed
The data accessing speed
is slower as compared to
SSD.
The data accessing speed is much higher as
compared to HDD.
Performance
The performance suffers
because of fragmentation.
The performance does not suffer because of
fragmentation.
Suitable for
HDDs are suitable for
•Extensive storage
•Long-term storage
SSDs are suitable for
•Fast data retrieval
•Laptop or desktop because of low power
consumption and size.

Flash Disks
Compact Flash (USB drives), memory sticks and other
compact media (e.g., micro SD cards) are increasing
versatile and vary in capacity.
They are very useful to have and can fit in your wallet or on
a keychain. These attach through USB or special drives.
Prices vary with the capacity (amount of storage space); you
can get a relatively inexpensive one that can hold a lot of
data.

Optical disks storage
Optical disk storage is a method of storing digital data on flat, circular
discs using lasers to read and write information. Optical disks are a
popular storage format for many applications, including archival
storage and data backup
Optical disk is a storage device that uses reflecting surfaces and laser
technology to read and write data on a disk. With optical storage, data
is burned into the storage medium using beams of laser light. The
burns form patterns of small pits in the disk surface to represent data.
Optical media are very durable, but they do not provide the flexibility
of magnetic media for changing the data once they are
stored.

i. CD-ROM (Compact Disk Read-
Only Memory)
CD-ROM (Compact Disk Read-Only Memory) is another
form of secondary storage, that is a low-cost storage
medium with a very large capacity.
Unlike other disk storage, CD-ROM is a WORM (Write
Once Read Many times) device i.e. it is a read only storage
device. This means that like ROM, the disk comes with
information already stored on it.
In terms of capacity, a single CD-ROM may store up to 600
megabytes.

ii. CD-R - Recordable
Also known as Recordable CDs, a CD drive unit
allows you to record data, music or video to your
own. (CD-R) is now becoming more widely used.
This storage combines the reliability and storage
capacity of CD-ROM with the flexibility of
magnetic disks in that users can store their own
information on them.
They are still slower to access than conventional
hard disks.

iii. CD-RW(Rewritable CD)
This type of optical disk can be erased and use to
rewrite new information.
This storage combines the reliability and storage
capacity of CD-ROM with the flexibility of magnetic
disks in that users can store their own information on
them.
They can store over 200 MB of data, and speed of
access to this data is faster than a floppy but slower than
a hard drive.
These take up much more storage space than data in
character format, such as in word-processed files.
They are still slower to access than conventional hard
disks.

iv. DVD (Digital Video Display)
DVD(Digital Video Display or Digital Versatile Disks) drives
are a common option on computers. are similar to CD-ROM (but
have a larger capacity) and are used for similar applications.
CD-ROMs are now being replaced by DVD-ROMs.
Software, especially with complex graphics (particularly
games) are distributed on DVD.
These are also used for distributing films as a rival to video
tapes. Also allow you to watch movies on your computer
screen.
DVD-ROM capacity ranges from 4.7 GB upwards (4.7x 2 or
4.7 x 4 GB).
A current PC will typically have a DVD drive which is also
capable of reading conventional CDs.

Writing a CD
It is not possible to write to a CD without
special hardware, a CD writer, popularly
known as a “CD burner”.
However, once you have written to a CD, it
cannot be erased and overwritten like a
diskette, unless you buy CD’s designed for re-
writing.
Even re-writable CD’s are not designed for
continual saving and overwriting

Computer Performance
Some of the factors which impact
computer’s performance, are such as:
–Data Bus
–CPU speed,
–RAM size, and
–the number of applications running
Explain how these affect computer
performance

Some of the factors which affect
Computer Performance
CPU Clock speed:
– The computer clock speed governs how fast the CPU
will run. The higher the clock speed the faster the
computer will work for you.
– The higher the MHz speed the faster the computer.
RAM size:
– As a rule the more memory you have the faster the
PC will appear to operate.
– Windows also uses the hard disk a lot, so logically
the faster the hard disk can operate then again the
faster the PC will appear to run.

Hard disk speed and storage:
– Hard disks are also measured by their speed, defined
by the disk access time, which is measured in
milliseconds.
– The smaller this access time the faster the hard disk
will store or retrieve data.
Free Hard Disk Space:
– To get the most out of your Windows based PC, you
not only need a fast hard disk but also a large hard
disk with plenty of "spare space".
– This is due to the fact Windows is constantly moving
data between the hard disk and RAM (Random
Access Memory).

Multitasking considerations(running more than
one program):
– Windows is a multitasking system, which means
that it can run more than one program at a time.
– However the more programs which are running at
the same time, the slower each one will run. To
some extent this slowing effect depends on what
each program is doing. Editing a large, full color
picture for instance can take up a lot of CPU
time.

Lecture 4b - Computer Elements_ Processing unit & memory.pdf

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Lecture 4b - Computer Elements_ Processing unit & memory.pdf