Computer Input output devices

1. UNIT 1: Computing Devices
LECTURER : BIJAY BHATTARAI
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2. Input & Output Devices 2
1. Key board:- Programs and data are entered through
keyboard . It contains alphabets digits function keys and
special characters By pressing a key an electronic signal
is produced and is detected by circuit called keyboard
encoder. Here it detects which key has been pressed.
Types :- PC keyboard , Enhanced Keyboard Multimedia
Keyboard

3. 2. Mouse :- Pointing device held on hand and moved
across flat surface, when user moves across surface
cursor moves on the direction of mouse’s
movements.
Types
 Mechanical Mouse
 Optical Mouse
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4. 3. Joy Stick:- Pointing device and performs like
mouse , it has spherical ball at its upper and lower
ends and moves in all direction. Inside it circuit
detects and measures the movement from central
position.
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5. 4. Voice Input System :- It converts the voice input into
electrical signals by comparing the electrical patterns produced
by the speakers voice with the set of pre-recorded patterns.
This device is beneficial for busy person and disable person.
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6. 5. Scanners :- Scanners are capable of
entering information directly into the computers
This provides faster and more accurate data
entry. This data is recorded on the basis of
width and space between the axis. This can
electronically capture text and images and
convert into computer readable form in binary
form as boxes of those images and text called
bit map and displayed on the screen.
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7. 6. Light Pen :- It is pointing device and used to select an option on
a screen and is capable of sensing a position in the CRT screen
when its tip touches the screen. The photocell sensing elements
detect the light coming from the screen and signal is sent to the
processor.
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8. Track Ball :-Pointing device that contains socket with ball which
is rolled manually to move the cursor on the screen, it also
contains sensor and it detects the movement of the ball.
Generally user uses thumb or finger.
Types
 Small trackball : used for portable devices.
 Large trackball :- used for desktop computers and for CAD
work.
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9.  Touch Screen :- It is a pointing device that is
used to enter data such as text pictures and
images by touching the screen. It enables
direct interaction with computer by touching the
screen.
 Uses
Mobile Technology , Pads ATMs PDA and gaming
devices.
Types
 Surface wave technology :- It uses ultrasonic
waves which are absorbed when they pass
through the touchscreen pad. Then these
absorbed waves are sent to the controller for
further processing . It is disturbed by dust and
water.
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10.  Capacitive Technology :- Uses indium tin oxide
material coated on touchscreen for providing
continuous electric charge. It has circuit as each
corner, when user touches screen , a small
amount of charge is absorbed at this point.
Finally this charge is transfer to controller for
further processing . Usually not disturbed by dust
or liquids.
 Resistive Technology:- The touch screen panel
generally consists of different layers which are
coated with very thin electrically conductive
metal ,when user touches at any point then there
is change is electric current
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11. The Output Accessories
 Output is anything that comes out of a computer, output can be
meaningful information which appears in the form of binary numbers
as characters, as pictures and as printed pages. An output device is
any machine capable of representing information from a computer.
 Hard Copy :- Information which has been recorded to the medium
which we can touch . Eg Paper or microfilm
 Soft Copy :- Output displayed in the screen and are temporary in
nature and vanish after use.
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12.  Monitor
It is a display screen and creates a visual display and is either built
into the CPU case or attached as an external devices by means of
cable.
 Types
 CRT(Cathode Ray Tube):- This display is made up of small
picture elements called pixel. Resolution is expressed as the
number of pixels on the screen. Monitor having more pixel
display more accurate image. It is large size consume high
power and fragile. For 1024*580 pixel size 1024 pixels
horizontally and 580 vertically. It has two types as Monochrome
monitor and colour monitor.
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13. CRT Monitor working mechanism
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14. Advantages of CRT monitor
 High contrast ratio and colour depth so recommended by graphic
designers.
 Provides change in the resolution without affecting the clarity of
the picture.
Disadvantages of CRT monitor
 It is very bulky and occupies more space
 Consumes more power and gets more heated too .
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15. Flat Screen Technologies
 It has eliminated the disadvantage of CRT and also have
replaced those and comes with laptops and other portable
devices.
Types
 LCD (Liquid Crystal Display) Monitor :- It uses liquid crystal
technology to display the images. Liquid chemical trapped in
tiny pockets between two pieces of glass. Each pocket of liquid
is covered both front and back by very thin wires. When a small
amount if current is passed to both wires it turns the chemical a
dark colour.
Advantages
 Small in size and light in weight to occupy space on desk.
 Low power consumption as less as liquid crystals need less.
Disadvantages
 Images looks blur as resolution is changed to that of fixed
resolution. Quality is not constant when viewed from different
angles.
 The clarity of images gets reduced when the images on an LCD
move at fast rate(frequency is monitor is changed).
 Weak colour quality as compared to CRT monitor.
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16.  Thin Film Transistor (TFT)Monitor
It is similar to LCD monitor but uses thin film transistor
along with liquid crystal to improve quality of the images.
For all pixels it uses small transistor and capacitor to
control separately.
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LED (Light Emitting Diodes) Monitor
These are the latest types in market today unlike LCD it uses back lightning
other than LCD as LCD uses Cold Cathode Fluorescent Light (CCFL). It
consumes less power than CRT and LCD and considered environment
friendly.
Advantages
• They produce images with higher contrast .
• They have less negative environmental impact when disposed.
• Lifespan and durability of LED monitors are more than LCD
• Do not produce much heat while running LED monitors
Disadvantages
They are expensive than other types of monitors.

17. Printers :- Printers are the most widely used outputs for applications it
creates hard copy of the information processed from computer system. It
is in the form of printed paper or any other form. Printers are of different
category fast printing slow printing multi-colour type single colour type.
Types
Impact Printer
Non Impact Printer
Impact Printer:- This type of printers makes contact with the paper, it
prints images or texts by pressing an inked ribbon against the paper with
the hammer like mechanism. The carbon copies can be produced using
impact printers
Non Impact Printers :- This type of printers do not strike characters against
ribbon. The main categories of non impact printers are ink-jet printer,
thermal printers and laser printers. They generate much less noise and
higher printing quality and carbon copies are not possible.
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18.  Impact Printers types
Dot Matrix Printers :-Impact printer with character printed on the paper
by the back and forth movement of the print head against the ribbon
drenched in ink. The characters are formed out of dots and dots are
produced with the help of a metal pin brought forward by small
electromagnet .
Dot matrix printers are capable of producing carbon copies and ensure
reliable printing and appropriate for the content of printing is more
important than quality of printing.
Advantages
There is no need to provide single sheets as these printers take
continuous sheets. Dot matrix printers are cheap to use as the cost of
printing per page is very less. If the printer has not been in use for long
time ink ribbon remains preserved for the future use and does not dry
quickly.
Disadvantages
They produce a lot of noise while printing and have low printing speed .
They support only limited colours and need a lot of maintenance if
damage
Use
Even they are not used for precise work but they are still use in business
and industries as they are cheap and can produce carbon copies.
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19. Daisy Wheel Printers :- It is also called
character printer as it prints one character at a
time. It produces a very high quality print
because the character is formed with a single
impact. In this printer there is wheel with a set of
printing character. Once the required character is
positioned towards the paper the disk is struck by
a hammer which acts as print head. The striking
of hammer on the disk forces the disk to hit the
ink-soaked ribbon and it leaves the impression on
the paper.
Advantages
It allows the printing of character in different fonts
Capable of print text only.
Disadvantages
They are very noisy as well as very slow and can
print approx. 10 to 75 characters only
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20. Drum Printers :- These are the impact printers in
which characters are engraved on a cylindrical drum,
and is rotated around print head hammer. The paper
and the ink ribbon lei between the hammer and the
drum so when the character is to be printed the
hammer strikes the paper and forces it to hit the
ribbon. The ribbon in turn hits the character on the
drum and the impression of the character is formed on
the paper.
Advantages
Low cost high speed compared to impact printers and
don’t require feeding of paper
Disadvantages
Poor quality of printing and large noise production
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21.  Non Impact Printers :- These printers do not strike
characters against ribbon. The main categories of non
impact printers are ink-jet printers thermal printers and
laser printers. They generate much less noise and
higher printing quality, carbon copies are not possible.
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22.  Ink Jet Printers :- This printer prints by
forming small dots by tiny droplets of ink
with the help of nozzle. It can print high
quality print of images and graphics.
Inks comes in cartridges
 Advantages:- They are cheaper and
portable as compared to other non-
impact printers.
Disadvantages :-It has slow speed and
requirement of special ink for inexpensive
papers.
It requires some time to dry after printing .
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23.  Laser Printer :- This printer resembles the operation
of photocopy machine A laser beam is directed across
the surface of ta light sensitive drum and fired as
needed to record an image in the form of pattern of tiny
dots. The image is then transferred to the paper a
page at a time these printers have very high speed low
noise level low maintenance cost very high image
quality and excellent graphics quality.
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25.  Sound Cards and Speakers :- Sound Card enables the
computer to output sound through speakers connected
to the board to record sound input from a microphone
connected to the computer and manipulate sound
stored on a disk.
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26.  Plotters :- It is used for printing high quality
graphics and images it uses one or more pen to
produce a high quality drawing. These pens change
their position and draws continuous lines to produce
an image. Plotters are cheap for bigger images and
graphs but require separate pen for each colour. But
newly plotters use basic colours as cyan, magenta,
yellow and black . So plotters are faster than before
Types of Plotters
Drum Plotters
Flat-Bed Plotters
Ink Jet Plotters
Electro static Plotters
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27.  Drum Plotters :- In this plotter pen moves vertically along Y axis
and the paper wrapped on the drum moves horizontally along X
axis and graph of image is created.
 Flat Bed Plotter :- Here position of the paper is kept constant
and the pens are moved around in various direction to draw
graphs and images. So pen moves in both X and Y axis .
 Ink-Jet Plotters:- Here line for a solid colour output is drawn with
the help of spraying ink droplets on the paper they have high
speed and produce high quality plotting compared to others.
However nozzle may get blocked through which ink passes.
 Electrostatic Plotters :- Here electrostatic charges are used to
draw images and graphs, images and graphs are made up of
tiny dots on special papers and produce high quality and
resolution. Effective for engineering field.
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Drum plotter
Electrostatic Plotter
Flat Bed Plotter
Ink-jet plotter

29.  Projectors :- Device that is connected to computer
or video device for projecting an image or videos on big
screen. It projects larger size as compared to original
images. It consists of optical system a light source and
displays which contains images. They were initially
used for showing movie ,business presentations
purposes.
 Types
Ultralight Portable projectors :- Small size
Conference Room Projectors :- large size for business
meetings and gatherings
Fixed Installation Projectors :- Expensive one fixed
permanently at preferred location.
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30. Thank you
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