415 33 powerpoint-slides_chapter-2-input-output-devices_ch2_2

CHAPTER 2

INPUT AND OUTPUT
DEVICES

© Oxford University Press 2012. All rights reserved.

INPUT DEVICES
An input device is used to feed data and instructions into the
computer. In the absence of an input device, a computer would have
only been a display device.

INPUT DEVICES

Keyboard

Pointing
Devices

Hand Held
Devices

Optical
Devices

Audio/Visual
Devices

Mouse

Pen

Bar code readers

Track Ball

Touch Screen

Scanners

Track Pad

Joystick

OCR
OMR
MICR


KEYBOARD
With a keyboard , the user can type a document, use keystroke shortcuts, access
menus, play games and perform numerous other tasks. Most keyboards have
between 80 and 110 keys which include:
•Typing keys
•Numeric keys
•Function keys
Advantages: Easy to use and cheap
Disadvantages:
Keyboard cannot be used to draw figures
The process of moving the cursor to some other position is very slow. Mouse and
other pointing devices are more apt for this purpose


MOUSE
• The mouse is the key input device to be used in a graphical user interface (GUI).
The users can use mouse to handle the pointer easily on the screen to perform
various functions like opening a program or file.
• With mouse, the users no longer need to memorize commands, which was
earlier a necessity when working with text-based command line environment such
as MS-DOS.
Advantages:
Easy to use; Cheap; Can be used to quickly place the cursor
anywhere on the screen; Helps to quickly and easily draw figures;
Point and click capabilities makes it unnecessary to remember certain commands
Disadvantages:
Needs extra desk space to be placed and moved easily
The ball in the mechanical mouse must be cleaned to remove dust from it

TRACKBALL
A trackball is a pointing device which is used to control the position of the cursor
on the screen. These are usually used in notebook and laptop computers where it
is placed on the keyboard. The trackball is nothing but an upside-down mouse
that rotates in place within a socket. The user rolls the ball to position the cursor
at an appropriate position on the screen and then clicks one of the buttons to
select objects or position the cursor for text entry.
Advantages:
Trackball provides better resolution; Occupies less space
Easier to use as compared to mouse as its use involves
less hands and arms movements
Disadvantage:
The trackball chamber is often covered with dust, so it must be cleaned regularly


TOUCHPAD
A touchpad (or track pad) is a small, flat, rectangular stationary pointing device
with sensitive surface of 1.5 or 2 inches square. The user has to slide his finger
tips across the surface of the pad to point to a specific object on the screen.
The surface translates the motion and position of user’s fingers to a relative
position on the screen. There are also buttons around the edge of the pad that
work like mouse buttons. Touchpad is widely used in laptops and is built-in on
the keyboard.
Advantages:
Occupies less space
Easier to use as compared to mouse as its use involves
less hands and arms movements
It is built-in the keyboard, so no need to carry an extra device separately

Joystick is a cursor control device widely used in computer games and CAD/CAM
applications. It consists of a hand-held lever that pivots on one end and transmits
its coordinates to a computer. It has one or more push-buttons, called
switches, whose position can also be read by the computer.
A stylus is a pen-shaped input device used to enter information or write on the
touch screen of a phone. Stylus is a small stick that can also be used to draw
lines on a surface as input to a computer, choose an option from a menu, move
the cursor to another location on the screen, take notes and create short
messages. The stylus usually slides into a slot built into the smart phone for that
purpose.
A touch screen is a display screen which can identify the occurrence
and position of a touch inside the display region. The user can touch
the screen either by his finger or by using a stylus. These displays
can be connected to computers, laptops, PDAs, cell phones etc.

BARCODE READERS
A barcode reader (or price scanner or point-of-sale scanner) is a hand-held input
device which is used to capture and read information stored in a barcode. A
barcode reader consists of a scanner, a decoder, and a cable used to connect the
reader with a computer.
The barcode reader merely captures and translates the barcode into numbers
and/or letters. To make use of the information captured it must be connected to a
computer for further processing. For this purpose, the barcode reader is
connected to a computer through a serial port, keyboard port, or an interface
device called a wedge.
Advantages:
Cheap
Portable
Used to read data stored in bar codes
Handy and easy to use

IMAGE SCANNER
•It is a device that captures images, printed text, handwriting from different
sources and converts it into a digital image for computer editing and display.
• Scanners come in hand-held, feed-in, and flatbed types.
•In the flat bed scanner, the object to be scanned is placed on a glass pane and a
sensor and light moves along the pane, reflecting off the image placed on the
glass.
•A hand image scanner has to be manually moved across an object or image to
be scanned. The scanner produces light from green LEDs which highlight and
scan the image onto a computer for further processing.
•Film scanners are usually used in photography and slides. The slide or negative
film is first inserted in strips of six or less frames into the film scanner, and then
moved across a lens and censor to capture the image.


Optical Character Recognition (OCR)
OCR is the process of converting printed materials into text or word processing
files that can be easily edited and stored. The steps involved in OCR include:
• Scanning of the text character-by-character
• Analyzing the scanned-in image to translate the character image into character
codes (ex ASCII)
Advantages:
Printed documents can be converted into text files
Advanced OCR can recognize handwritten text and convert them into computer
readable text files

Printed
Documents

OCR
Technolog
y

Disadvantages:
OCR cannot recognize all types of fonts

Computer
readable
Text files of
size 2-3KB
per page

Scans the documents and
makes a bitmap of size 50150KB per page

Documents that are poorly types or have strikeover cannot be recognized
Very old documents when passed through OCR may not have an exact copy of
the text file.


OPTICAL MARK RECOGNITION
OMR is the process of electronically extracting data from marked fields, such as
checkboxes and fill-infields, on printed forms. The optical mark reader is fed with
an OMR sheet to detect the presence of a mark by measuring reflected light levels.
The OM reader interprets this pattern marks and spaces and stores the interpreted
data in computer for storage, analysis and reporting.
The error rate for OMR technology is less than 1%.
It is used for applications in which large numbers of hand-filled forms have to be
quickly processed with great accuracy, such as surveys, reply cards,
questionnaires, ballots or sheets for multiple choice questions.
Advantages:
Optical mark readers works with a very fast speed. They can read
up to 9,000 forms per hour
They are accurate machines with error rates of just 1%

Fourth Generation (1971-1989) Microprocessors
The microprocessor started the fourth generation of computers with thousands of integrated circuits built onto a single silicon chip.

MAGNETIC INK CHARACTER READER (MICR)

• MICR is used to verify the legitimacy or originality of paper documents,
especially checks.
• MICR consists of magnetic ink printed characters which can be recognized
by high speed magnetic recognition devices .
• The printed characters provides important information (like check number,
bank routing number, checking account number and in some cases the
amount of the check) for processing to the receiving party.
• MICR is widely used to enhance security, speed up the sorting of
documents and minimize the exposure to check fraud.

Audio Devices
Audio devices are used to either capture or create sound. They enable computers
to accept music, speech or sound affects for recording and/or editing.
Microphone and CD player are examples of two widely used audio input devices.
Microphone feeds audio input to the computer. The computer must have a sound
card to convert analog signals generated through microphone into digital data so
that it can be stored in the computer. When the user wants to hear the prerecorded audio input, the sound card converts the digital data into analog signals
and sends it to the speakers.
Advantages:
Audio devices can be used by people who have visual problems; It is best used in
situations where users want to avoid i/p through keyboard or mouse
Disadvantages:
Audio input devices are not suitable in noisy places; With audio input devices it is
difficult to clearly distinguish between two similar sounding words like “sea” and
“see”


Video Input Devices
Video input devices are used to capture video from the outside world into the
computer.
Digital camera is used to capture images or videos. It digitizes the image or video
and stores them on a memory card. The data can then be transferred to the
computer using a cable which connects computer to the digital camera.
Web cameras also capture videos which can be transferred via internet in real
time.
Advantages:
Video input devices are very useful for applications like video conferencing
Video input devices can be used to record memorable moments in one’s life
Video input devices can be used to check security
Disadvantages:
Videos and images captured using video input devices have a very big file size
and there must be compressed before being stored on the computer.

CLASSIFICATION OF COMPUTERS
Computers can be broadly
OUTPUT DEVICES classified into four categories based on their speed, amount of data that they can hold and price.

Any device that outputs/gives information from a computer is called an output
device.
Output devices are electromechanical devices which accept digital data from the
computer and converts them into human understandable language.
SOFT COPY DEVICES
Soft copy output devices are those output devices which produce an electronic
version of an output. For example, a file which is stored on hard disk, CD, pen
drive, etc and is displayed on the computer screen (monitor).
Features of a soft copy output include:
The output can be viewed only when the computer is on.
The user can easily edit the soft copy output
Soft copy cannot be used by people who do not have a computer
Searching data in a soft copy is easy and fast.
Electronic distribution of a soft copy is cheaper. It can be done easily and quickly

CATHODE RAY TUBE MONITORS
•CRT monitors work by firing charged electrons at a phosphorus film. When
electron hit the phosphor coated screen, it glows thereby enabling the user to see
the output.
•In a cathode ray tube, the "cathode" is a heated filament which is placed in a
vacuum created inside a glass "tube." The "ray" is a stream of electrons which
comes out from a heated cathode into the vacuum.
•The focusing anode focuses the stream of electrons to form a tight beam which
is then accelerated by an accelerating anode.
•This tight, high-speed beam of electrons flies through the vacuum in the tube and
hits the flat screen at the other end of the tube.
•This screen is coated with phosphor, which glows when struck by the beam,
thereby displaying the picture which the user sees on the monitor.

CATHODE RAY TUBE MONITORS

Schematic diagram of a Cathode Ray Tube


LIQUID CRYSTAL DISPLAY MONITORS
• LCD monitor is a thin, flat electronic visual display that uses the light modulating
properties of liquid crystals which do not emit light directly.
•LCD screens are used in a wide range of applications ranging from computer
monitors, television, instrument panels, aircraft cockpit displays, signage, to
consumer devices like such as video players, gaming devices, clocks, watches,
calculators, and telephones.
•Liquid crystal display technology is based on blocking light. The LCD consists of
two pieces of polarizing filters (or substrates) that contain a liquid crystal material
between them. A backlight creates light which is made to pass through the first
substrate. Simultaneously, the electrical currents cause the liquid crystal
molecules to align to allow varying levels of light to pass through to the second
substrate and create the colors and images are seen on the screen.


LIQUID CRYSTAL DISPLAY MONITORS

Schematic diagram of a Liquid Crystal Display Monitor


PLASMA MONITORS
•Plasma monitors are thin and flat monitors widely used in TVs and computers. The plasma
display contains two glass plates that have tiny cells filled with xenon and neon gas.
•The display electrode is covered by a magnesium oxide protective layer and is arranged in
horizontal rows along the screen while the address electrodes are arranged in vertical
columns thereby forming grid like structure.
•To ionize the gas in a particular cell, the electrodes that intersect at that cell are charged at
least thousands of times in a small fraction of a second
• An electric current begins to flow through the gas in the cell. The current creates a rapid
flow of charged particles thereby stimulating the gas atoms to release ultraviolet photons.
•When these UV photons hit a phosphor atom in the cell, one of the phosphor's electrons
jumps to a higher energy level and the atom heats up. When the electron falls back to its
normal level, it releases energy in the form of a visible light photon.

PROJECTOR
A projector is a device which takes an image from a video source and projects it
onto a screen or other surface. These days, projectors are used for a wide range
of applications varying from home theater e systems to organizations for
projecting information and presentations onto screens large enough for rooms
filled with people to see.


SPEAKERS
Today all business and home users demand sound capabilities and thus
different types of speakers to enable users to enjoy music, movie, or a game
and the voice will be spread through the entire room. With good quality
speakers, the voice will also be audible even to people sitting in another or
room or even to neighbors.
However, in case the user wants to enjoy loud music without disturbing the
people around him, he can use a headphone.
Another device called headset was developed to allow the users to talk and
listen at the same time, using the same device.


HARD COPY OUTPUT DEVICES
Hard copy output devices produces a physical form of output. For example, the
content of a file printed on a paper is a form of hard copy output.

PRINTERS
Printer is a device that outputs text and graphics information obtained from the
computer and prints it on to a paper. Printers are available in the market in a
variety of size, speed, sophistication, and cost. The qualities of printer which are
of interest to users include:
Color: Colored printouts are needed for presentations or maps and other pages
where color is part of the information. They are more expensive,


PRINTERS contd.
Memory: Most printers have a small amount of memory that can be
expanded by the user. Having more memory makes enhances the speed
of printing
Resolution: The resolution of a printer means the sharpness of text and
images on paper. It is usually expressed in dots per inch (dpi). Even the
least inexpensive printer provides sufficient resolution for most
purposes at 600 dpi.
Speed: Speed means number of pages that are printed in one minute.
While high speed printers are a little expensive, the inexpensive printers
on the other hand can print only about 3 to 6 sheets per minute. Color
printing is even slower.

PRINTERS contd.

Impact Printer. They create characters by striking an inked ribbon against the
paper. Ex., dot-matrix printers, daisywheel printers, and most types of line printer.
Non Impact Printer: Non-impact printers are much quieter than impact printers as
their printing heads do not strike the paper. They offer better print quality, faster
printing and the ability to create prints that contain sophisticated graphics.
Non-impact printers use either solid or liquid cartridge-based ink which is either
sprayed, dripped or electro statically drawn onto the page. The main types of nonimpact printer are: inkjet, printer, laser printer and thermal printer.


DOT MATRIX PRINTER
A dot matrix printer prints characters and images of all types as a pattern of dots.
It has a print head (or hammer) that consists of pins representing the character or
image. The print head runs back and forth, or in an up and down motion, on the
page and prints by striking an ink-soaked cloth ribbon against the paper, much
like the print mechanism on a typewriter.
Advantages
It can produce carbon copies; offers lowest printing cost per page;
widely used for bulk printing where quality of the print is not of
much importance; is cheap; When the ink is about to finish, the
printout gradually fades rather than suddenly stopping partway through a job
It can use continuous paper rather than individual sheets, making them useful for
data logging.
Disadvantages
It creates a lot of noise when the pins strike the ribbon to the paper.
It can only print lower-resolution graphics, with limited quality
It is very slow
Poor print quality

DAISY WHEEL PRINTER
•Daisy wheel printers use an impact printing technology to generate high-quality
output comparable to typewriters but three times faster.
•The print head of a daisy wheel printer is a circular wheel, about 3 inches in
diameter with arms or spokes. The characters are embossed at the outer end of
the arms.
•To print a character, the wheel is rotated in such a way that the character to be
printed is positioned just in front of the printer ribbon.


• The spoke containing the required character is then hit by a hammer
thereby striking the ribbon to leave an impression on the paper placed
behind the ribbon. Movement of all these parts is controlled by
microprocessor in the printer.
• The key benefit of using a daisy wheel printer is that the print quality is
high as the exact shape of the character hits the ribbon to leave and
impression on paper.


LINE PRINTER
Line printer is a high speed impact printer in which one typed line is printed at a
time. The speed of a line printer usually varies from 600 to 1200 lines-per-minute
or approximately 10 to 20 pages per minute. They are widely used in datacenters
and in industrial environments. Band printer is a commonly used variant of line
printers.
Band Printer: A band printer (loop printer) is an impact printer . The set of
characters are permanently embossed on the band and this set cannot be
changed unless the band is replaced. The band itself revolves around hammers
that push the paper against the ribbon, allowing the desired character to be
produced on the paper. However, band printers cannot be used for any graphics
printing as the characters are predetermined and cannot be changed unless the
band is changed.

Band Printer

Schematic diagram of a band printer


INKJET PRINTERS
• In inkjet printers , the print head has several tiny nozzles, also called jets.
•As the paper moves past the print head, the nozzles spray ink onto it, forming the
characters and images.
•The dots are extremely small (usually between 50 and 60 microns in diameter)
and are positioned very precisely, with resolutions of up to 1440x720 dots per
inch (dpi).
•There is usually one black ink cartridge and one so-called color cartridge
containing ink in primary pigments (cyan, magenta, and yellow).


INKJET PRINTERS Contd.
• While inkjet printers are cheaper than laser printers, they are more expensive
to maintain. The cartridges of inkjet printers have to be changed more
frequently and the special coated paper required to produce high-quality
output is very expensive. So the cost per page of inkjet printers becomes ten
times more expensive than laser printers. Therefore, inkjet printers are not
well-suited for high-volume print jobs.


LASER PRINTER
•It is a non-impact printer that works at a very high speed and produces high
quality text and graphics.
• It uses the photocopier technology. When a document is sent to the printer, a
laser beam "draws" the document on a drum (which is coated with a photoconductive material) using electrical charges.
• After the drum is charged, it is rolled in toner (a dry powder type of ink).
• The toner sticks to the charged image on the drum.
• The toner is transferred onto a piece of paper and fused to the paper with heat
and pressure.


LASER PRINTER Contd.
• After the document is printed, the electrical charge is removed from the
drum and the excess toner is collected.
• While color laser printers are also available in the market but users prefer
only monochrome printers because a color laser printer is up to 10 times
more expensive than a monochrome laser printer.


PLOTTERS
A plotter is used to print vector graphics with a high print quality. They are widely
used to draw maps, in scientific applications and in applications like CAD, CAM
and CAE
A drum plotter is used to draw graphics on a paper that is wrapped around a
drum. It works by rotating the drum back and forth to produce vertical motion. The
pen which is mounted on a carriage is moved across the width of the paper.
Hence, the vertical movement of the paper and the horizontal movement of the
pen create the required design under the control of the computer.


In a flatbed plotter, the paper is spread on the flat rectangular surface of the
plotter and the pen is moved over it. Flatbed plotters are less expensive and
used in many smaller computing systems. In this type of plotter, the paper is
not moved rather plotting is done by moving an arm that moves a pen over
paper.


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