3 io devices
TRANSCRIPT
Input/output Devices
The I/O devices commonly called peripherals
connected to a computer system provide an
efficient mode of communication between the
computer and the external world.
The user can enter programs and data using the
input device on a terminal and can execute the
programs and display the output result using an
output device connected to a terminal.
Input Devices
The objective of an input device is to capture
raw data and convert it into computer-usable
form as quickly and efficiently as possible.
Input devices can be classified according to:
Mode of input (eg: mechanical, audio, visual
etc.)
Nature of input (discrete – key presses or
continuous – mouse movement)
Punched Cards
A punched card is a piece of stiff paper that
contains digital information represented by the
presence or absence of holes in predefined
positions.
Early digital computers used punched cards,
often prepared using keypunch machines , as the
primary medium for input of both computer
programs and data.
Keyboards
A keyboard is the set of typewriter-like keys that enables us toenter data into a computer.
The keys on the computer keyboards are often classified as:Alphanumeric keys – Letters and numbers.Punctuation keys – Comma, period, semicolon and so on.Special keys – Function keys, control keys, arrow keys, caps lockkey and so on.
The output of the key switches are fed into electronic circuitryknown as the keyboard encoder which converts them intobinary-coded values. The values are then fed into the computerwhich interprets the key which was pressed.
Mouse
A mouse is a pointing device that is most oftenused with a personal computer and which can fitcomfortably in a user’s palm.
A mouse consists of an object held under one ofthe user’s hands, with one or more buttons.
Moving a mouse along a flat surface can movethe on-screen cursor to different items on thescreen. Items can be moved or selected bypressing the mouse buttons.
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Mechanical Mouse: It has a rubber or metallic
ball on its underside that can roll in all direction.
Mechanical sensors within the mouse detects the
direction of the rolling ball.
Optical Mouse: It uses a laser beam to detect
direction of rolling.
Continued...
Mechanical mouse shown with
the top cover removed
A standard wireless mouse with
connector
Computer mouse built between 1986 to 2007
Scanner
A scanner is a device that optically scans images,
printed text, handwriting, or an object, and
converts it to a digital image.
Flat-bed Scanner
Hand-held Scanner
Drum Scanner
Continued...
Optical Mark Reader (OMR): An OMR is a special
scanning device that can read carefully placed pencil
marks on specially designed documents. OMR is
frequently used in forms, questionnaires and answer-
sheets.
Continued...
Magnetic Ink Character Recognition (MICR): MICR is an
input device widely used by banks to process large volume
of checks and deposit forms. It consists of special ink called
magnetic ink, used to write characters on the check and
deposit forms to be processed by MICR. It is capable of
recognizing characters written on paper by magnetic ink. It
interprets the characters and sends the corresponding data
directly to the computer for processing.
Joystick
A joystick is also a pointingdevice which is providedwith a spherical ball onwhich a stick is mounted andmoves in a socket. The usermove the spherical ball withthe help of the stick withhis/her hand. The stick can bemoved forward or backward,left or right to positioned thecursor at the desired location.It is provided with a buttonon the top to select theoption.
Output Devices
An output device is a peripheral device
used to communicate the results of
data processing carried out by a
computer which converts the
electronically generated information
into human-readable form.
Monitors
A monitor is an electronic visual display for computers. It
is used to display the video and graphics information
generated by the computer through a video card. Images
are represented on monitors by individual dots called
pixels. A pixel is the smallest unit on the screen that can
be turned on and off or made different shades. The density
of the dots determines the clarity of the images, the
resolution. Monitors are very similar to televisions but
usually display information at a much higher resolution.
Monitors come in two major types:CRT (Cathode ray tube)TFT-LCD (Thin film transistor – Liquid crystal display)
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CRT (Cathode ray tube): CRT is a vacuum tube
containing one or more electron guns and a fluorescent
screen used to view images. A CRT works by moving an
electron beam back and forth across the back of the
screen. Each time the beam makes a pass across the
screen, it lights up phosphor dots on the inside of the
glass tube, thereby illuminating the active portions of
the screen. By drawing many such lines from the top to
the bottom of the screen, it creates an entire screenful of
images. CRTs are relatively heavy, bulky and take up lot
of space in comparison to other display technologies.
Continued...
TFT-LCD (Thin-film transistor – Liquid crystal display): A TFT-
LCD is a flat-panel display, that has replaced the old CRT. It uses
thin-film transistor technology in which a separate transistor
works for each pixel along with the liquid crystal material. The
liquid crystal material exhibits properties of both a liquid,
because of its ability to change quickly, and a crystal, because of
its ability to remain in an arranged position. The transistor applies
the voltage to the pixel, determining its colour and intensity. TFT
monitors consumes less power, deliver sharp images and looks
more elegant than CRT monitors. However, they tend to offer
relatively poor viewing angles. It means they look best when
viewed head-on, and if viewed from the side, it can be difficult to
see.
Printers
A printer is a peripheral device that produces a
text or graphics of documents stored in
electronic form, usually on paper.
Two broad categories are:
Impact Printers
Non-impact Printers
Impact Printers
Impact printers are the oldest printing technology
that work by banging a head against an ink
ribbon to produce a mark on the paper. The three
most common forms of impact printers are:
Dot-matrix printers
Daisy-wheel printers
Line printers
Dot-Matrix Printers
Dot-matrix printers, are so named because printer characters are in
the form of group of dots. Each dot is produced by moving a metal
rod, called wire, that strikes a ribbon against the paper.
Its features are:
Low purchase cost.
Lower quality with low resolution.
Generate carbon copies.
Good, reliable and ideal for situations where printed contents is
more important than quality.
Noisy
Slow speed.
Daisy-Wheel Printers
Daisy-wheel printers, consist of a circular wheel about 3inches in diameter
with arms or spokes. The character shape are embossed at the outer ends of the
spokes. The shape of the printer wheel resembles the petals of a daisy flower
and hence, it is named daisy wheel printer.
To print a character, the daisy wheel rotates so that the required character is
positioned just in front of the printer ribbon. The spoke containing the
character is hit by hammer which strikes the ribbon leaving an impression on
the paper.
Its features are:
Better printing quality than dot-matrix printers.
Font types can be changed by changing the wheel.
Low speed & noisy.
Line Printers
Line-printers are somewhat similar to the daisy-wheel printer. Instead of a
print wheel, line printers have a mechanism that allows multiple characters to
be simultaneously printed on the same line.
The mechanism uses a large spinning print drum. As the drum is rotated over
the paper’s surface, electromechanical hammer behind the paper pushes the
paper along with a ribbon onto the surface of the drum marking the paper with
the shape of the character on the drum.
Its features are:
Faster than dot-matrix and daisy-wheel printers.
Noisy.
Limited multi-font capability.
Lower print quality
Non-impact Printers
Non-impact printers does not operate by striking
a head against a ribbon, as there is no direct
contact between the printhead and the paper. The
three most common forms of non-impact printers
are:
Ink-jet printer
Thermal printer
Laser printer
Ink-jet Printers
Ink-jet printers, creates a digital image by spraying droplets of ink onto the paper. The
characters are produced as a result of electrically charged or heated ink being sprayed
from fine nozzles onto the paper. Individual nozzles produces high resolution (upto 400
dpi) dot-matrix characters.
Ink-jet printers can use coloured cartridges to create coloured images. The printer can
generate upto 200 characters per second, and allows for good quality and cheap
printing.
Its features are:
Less noisy
Lower cost per page
Expensive
With time, the ink-jet prints fades and colour balance may get changed.
Fine ink-jet nozzles are prone to blocking which requires periodic cleaning.
Thermal Printers
Thermal printers, uses heat that adheres a wax-based ink onto paper. It has a
thermal printhead that melts wax-based ink from the ribbon onto the paper.
When cool, the wax ink becomes permanent. These printers are popular for
printing bar codes, price tags etc.
Its features are:
Quiet with good printing speed.
Good quality printouts.
Weather resistant as it can last for longer time even with extreme
temperatures.
Light weight and easy to carry.
It requires a specialized paper, which are more expensive than normal bond
paper.
Unable to print coloured images.
Laser Printers
Laser printers, rapidly produces high quality text or graphics on plain paper. When a
document is sent to the printer, a laser beam draws the document on a selenium-coated drum
using electrical charges. After the drum is charged, it is rolled in tonner (a dry powder type
ink), which is picked up by the charged portions of the drum. The tonner is then transferred
onto the piece of paper through the combination of heat and pressure. After the document is
printed, the electric charge is removed from the drum and the excess toner is collected.
Its features are:
Very good printing quality.
High printing speed.
Noiseless.
Light weight and compact.
Colour printing is possible.
Cartridges are expensive.
Carbon copies cannot be generated simultaneously.