The document discusses various input and output devices used in computers. It describes common input devices like the keyboard, mouse, joystick, scanners, microphones, and digital cameras. It explains how these devices work and their advantages and disadvantages. The document also covers various types of output devices including monitors, printers, plotters and speakers. It provides details on CRT and LCD monitors and different types of printers like impact, non-impact, inkjet and laser printers.

1. BY-SRISHTI SAXENA
CLASS-IX

2.  The keyboard
 The mouse
 Joystick
 The scanner
 1. Hand –held scanners
 2. Flatbed scanners
 3. Drum scanners
 Optical character reader
 Magnetic ink character reader
 The light pen
 Bar code readers
 Microphone
 Digital camera

3.  Monitors
 1. Cathode ray tube
 2. Liquid crystal display
 Printers
 Impact printers
 Non-impact printers
 1. Inkjet printers
 2. Laser printers
 Plotters
 Speakers

4.  The input is responsible for accepting
input i.e., data and instructions from the
user. This work is accomplished with the
help of input devices. Device , in general ,
refers to an equipment.
 Over many years , many input devices
have been built in many forms for many
special purposes .For instance , keyboard is
used for different purpose and a mouse or
a trackball is used for different purpose .

5.  Keyboard is a typewriter like device which is
used to type in the letters , digits and commands
. A keyboard contains a matrix of switches (one
switch per key).Each key , when pressed , sends a
digital code to the computers that determines
which key has been pressed e.g., if you press ‘A’
when caps lock key is on , a code 01000001 is
sent to computer ;computer than translates this
code to determine that you pressed ‘A’.

6.  Advantages
 Reliable way of inputting text and numbers.
 Available in variety of formats.
 Disadvantages
 Not useful for entering some specific type of data .
 Very slow while accessing menu options or selecting
various objects screen.
 Not much useful for enlarging or changing sizes of
windows on screen .
 Very slow while moving windows or other objects.

7.  The mouse is a pointing device with a
roller on its base. Mouse controls
movement of pointer 98also called mouse
pointer) on screen.When a mouse moves
on a flat surface , the cursor on the screen
also moves in the direction of mouse’s
movement . A mouse generally has two or
three buttons and it may or may not have
a wheel.

8.  Advantages
 Ideal for pointing objects/options on desktop
computers .
 Most familiar and easy to use pointing device .
 Disadvantages
 Need a flat space close to computer.
 A mouse can’t easily be used with a laptop or a
notebook or a palm top computers .

9.  Joysticks are often used for playing
computer games such as flight
simulators . They input directional
data like mouse but work by switches
being closed as the joystick is moved
left or right and up or down .Mini
finger – controlled joysticks can be
used to control a laptop cursor.

10.  Advantages
 Easy to learn to use.
 It is not costly.
 Disadvantages
 Movement is offered only in forward , backward ,
left and right directions , so diagonal movements
create problems at times .

11.  A scanner is a device similar to a photocopier . A
photocopier prints the given printed image/page on a
paper . And a scanner creates a electronic form of the
printed image ,which can later be manipulated ,
changed and modified according to the requirements .
The scanners can convert any image into electronic
form by shining light on to the image and sensing the
intensity of reflection at every point .Scanners come
in the variety of sizes from hand-held models to
desktop models.

12.  Hand – held scanners are very small which
can be held n a hand . These are less
expensive but less wide . Hence , in order
to scan a single page image , multiple
passes are required . But their handiness
is a major advantage .

13.  Flatbed scanners are larger and more
expensive scanners but they definitely
create higher quality images . These
scanners have a flat surface an which the
printed image to be scanned , is placed .
(Similar to the way a page is placed on a
photocopier). Flatbed scanners can scan a
page in a single pass .

14.  Drum scanners are medium – size
scanners with a rolling drum . The
sheet is fed through the scanners so
that the drum rolls over the entire
sheet to be scanned . ( Just as the
sheets are fed in a fax machines).

15.  Advantages
 Flatbed scanners are very accurate and can produce
images with a far higher resolution than a digital
camera.
 Any image can be convertd from paper into digital
format and later enhanced and used in order computer
documents .
 Disadvantages
 Images can take up a lot of memory space.
 The quality of the final image depends greatly upon
the quality of original documents.

16.  An optical character reader is used to read character of
special type font(or fonts0 printed on conventional
paper with conventional ink. These days , OCRs are
capable of reading/identifying handwritten text also .
The printed characters are examined by passing them
under a strong light and a lens system , which
differentiates light(no ink) from inked areas , and a
logical system which attempts to determine which of
the possible characters is being examined .

17. Advantages
OCR is faster than typing a document which is in
printed form or hand-written form.
Converted text is editable in word processors.
Advanced version can even recreate tables , columns
and even produce web pages.
Disadvantages
You need to buy a scanner or OCR software.
It is not completely accurate and text would need proof –
reading afterwards.

18.  In this method , human readable characters are
printed on documents (such as cheques ) using a
special magnetic ink. Special font has been set for
these characters by American Banking Association .
 Characters are printed using a special ink called
magnetic ink(that contains iron oxide).MICR reads
these characters by magnetizing the ink and by
examining the shape of the character . This method ,
besides saving time , also ensures the accuracy of data
entry.

19.  Advantages
 Documents prepared for MICR are difficult to forge.
 Documents can still be read after being folded or split
etc.
 Disadvantages
 MICR readers and encoders are expensive.
 The system can only accept few characters.

20.  A light pen is also a pointing device. The light pen
consists of a photocell mounted in a pen-shaped tube
.When the pen is brought in front of a picture element
of the screen , it senses light coming from a limited
field of view. The light coming from the screen causes
the photocell to respond by generating a pulse . This
electric response is transmitted to a processor that
identifies the pixel the light pen is pointing to.
Clicking is performed by pressing the pen on the
screen . Thus , to identify a specific location, the light
pen is very useful . But the light pen provides no
information when held over a blank part of the screen
because it is a passive device with a sensor only.

21.  Advantages
 Easy to use.
 Useful for programs like CAD(Computer Aided
Design) for changing shape , size , location , colours
etc, of the screen image.
 Can directly draw on screen.
 Disadvantages
 Not very accurate while drawing.
 Expensive compared to alternate pointing devices like
mouse.
 Tiresome after long usage hours.

22.  A bar code reader is also one of the most widely used
input devices . As you must be aware that a bar code is
a pattern of printed bars on various types of products .
You may even see a bar code printed at the back cover
of this book . A bar code reader emits a beam of light (
generally a laser beam) which reflects off the bar code
image . A light sensitive detector in the bar code reader
then identifies the bar code image by recognising
special bars at the both ends of the image .Once the
bar code is identified , the bar pattern is converted into
a numeric code that can be processed later in any
manner.

23.  Advantages
 Fast and reliable method of inputting data.
 Can even read from curved or upside down
surfaces.
 Disadvantages
 Input is limited to a number code.

24.  We can send sound input to computer through a
special input device called microphone or mic in
short. A mic converts the sound received into
computer’s format , which is called digitalized sound
or digital audio.
 A mic can work if your computer has a special
hardware known as sound card.
 Sound is used most often in multimedia , where the
presentation can benefit from recorded narration ,
music or sound effects.

25.  Advantages
 Useful for inputting audio / sounds which
can’t be input through other available input
devices.
 Disadvantages
 Needs specific and additional hardware
called soundcard which must be inserted in
motherboard.

26.  A camera that stores images digitally rather than recording
them on film is called digital camera.
 The light passing through the lens of digital camera is
digitalized by special servers that are sensitive to light . The
image formed is stored is camera’s storage memory.
 Once a picture has been taken , it can be downloaded to a
computer system , and than manipulated with the graphics
program and printed.
 The big advantage of digital cameras is that making photos
is both inexpensive and fast because there is no film
processing.

27.  The output unit is responsible for producing the
output in user readable form . Various output devices
like monitor , printer , plotter etc. make the output
unit of a computer.
 The function of an output device is to present
processed data to the user . The computer sends
output to the monitor if the user needs to see the
output . The output is send to the printer whenever the
output is needed in the hard copy form. The sound
output is processed with the help of speakers .
Graphics output is processed with the help of plotters.

28.  Monitor or screen is the most common form of output
from a computer . It displays information in a similar
way to that shown on a television screen . The picture
on a monitor is made up of thousands of tiny coloured
dots called pixels.
 The two most common types of monitor are a Cathode
- Ray Tube (CRT) and a Liquid Crystal Display(LCD)
monitor.

29.  The CRT works in the same way as
atelevision – it contains an electron
gun at the back of the glass tube . This
fires electron on the group of phosphor
dots , which coat the inside of the
screen . When the electrons strike the
phosphor dots they glow to give the
colours .

30.  Liquid crystal is the material used to create each pixel
on the screen . The material has a special property – it
can ‘ polarise ’ light depending on the electrical charge
upon it . This feature allows the pixels to be created .
Each tiny cell of liquid crystal is a pixel .
 TFT(Thin Film Transistor) is the device within each
pixel that sets the charge . And so sometimes they are
called ‘Liquid Crystal Display’ referring to the material
they use or they are called ‘TFT Displays’ referring to
the tiny transistors that make them work . LCDs use
much less power than a normal monitor .

31.  Advantages
 Relatively cheap and reliable .
 Can display text and graphics in a wide range of colours .
 As each task is processed , the results can be displayed
immediately on the screen .
 Quiet .
 Disadvantages
 No permanent copy to keep – the results will disappear
when the computer is switched off .
 Unsuitable for hours with visual problems .
 Only a limited amount of information can be displayed at
any one time .
 CRT screens are made of glass and can be very fragile .

32.  Printer is an output device used for creating
paper copies of output from the computer .
Printers can produce text and image on
paper .
 There are two types of printers used . They
are –
 Impact printers
 Non- impact printers

33.  In these printers , there is mechanical
contact between the print head and paper .
These come in a lot of varieties such as line
printers , drum printers , daisy wheel
printers , and dot matrix printers . Most
common impact printer in use today is Dot
matrix printer , which is being covered in
the coming lines .

34.  The dot matrix printer is a most popular serial
printer i.e., it prints one character at a time . In
DMPs , the printing head contains a vertical array
of pins . As the head moves across the paper ,
selected pins fire against an inked ribbon to form a
pattern of dots on the paper .These days 24 pin
DMPs are also available in the market offering
more quality and more features . There are 80
column DMPs and 132 column DMPs available in
the market .

35.  Advantages
 Low operating costs .
 Can print on continuous stationary .
 They are robust and can be used in dirty or harsh
conditions –you often see them in garages or factories .
 Using carbonated paper , DMPs can create carbon copies .
 Disadvantages
 Low resolution – print quality is too poor .
 Very slow –can be less than 100 characters per minute .
 Very noisy – can’t be used near a phone .
 Cnnot produce colour copies .

36.  In these printers , there is no
mechanical contact between the print
head and paper . The natural
limitations of speed in
electromechanical devices and cost
considerations have led to the
development of printers called non –
impact printers .

37.  An inkjet printer is any printer that fires
extrememly small droplets of the ink onto
paper to create impression of text or image .
The printhead of inkjet printers contains
tiny nozzles through which different
coloured inks can be sprayed onto paper to
form the characters or graphic images . The
ink of inkjet printer is stored in catridges .

38.  Good resolution – usually 300-600 dots per inch . This
means they can print good quality results .
 Cheap to buy .
 Small – ideal for home or offic .
 Lighter in weight than other printers .
 Fast compared to a dot matrix printer .
 Very quiet .
 Can print black and white and colour on the same
page .

39.  Slow compared to a laser printer .
 Colour printing can take 25-30 seconds each page .
 Overall , the catridges cost more per page than laser
printer catridges .
 Catridges need to be replaced more frequently than
those of a laser printer .
 Output is ink based and will smudge if the printout
gets wet .
 If left unused for long periods of time , the catridges
can easily dry out .

40.  These printers print in the same way as
photocopies do .The powered ink is
transferred to paper to form a text/image
pattern . It is then fixed by heat and
pressure .The laser printers are quiet and are
capable of producing very high point quality
.The speed of laser printers can be upto 10-
20 pages per minute . When used to print
bulk of papers , the laser printer produces
the cheapest cost per page printouts .

41.  Very high resolution – 600 to 1200 dots per
inch .
 High quality printouts .
 Very fast : 10 –20 pages per minute for
multiple copies .
 Almost silent .
 Running costs are low , although toner
catridges are expensive to replace , they last
a long time .

42.  Most expensive printer type to buy especially colour
lasers .
 Expensive to repair – lots of complex equipment
inside .
 Can’t use continuous or multi – part stationary to
create carbon copies .
 Only A4 or A5 paper can be used in most laser printers
although A3 is available .

43.  Many applications require a graphical
output apart from printed output .For
example , pie charts , bar charts and graphs
with annotations are useful representation
of information .Plotters are the output
devices that produce good quality drawings
and graphs . There are two types of plotters :
drum plotter and flat bed potter .

44.  Advantages
 Drawings are of the same quality as if an expert drew them .
 Larger sizes of paper can be used than would be found on
most printers .
 Disadvantages
 Plotters are slower than printers , drawing each line
separately .
 They are often more expensive to buy than printers .
 Although drawings are completed to the highest quality
they are not suitable for text although text can be produced
.
 There is a limit to the amount of detail these plotters can
produce .
 In recent years , cheaper printers that can handle A3 and
A2 sized paper have resulted in a decline in the need for
smaller plotters .

45.  Speakers receive the sound in form of
electric current from the sound card and
then convert it to sound format . The
speakers that are attached to the computer
are similar to the ones that are connected to
a stereo . The only difference is that the
computer system’s speakers are usually
smaller and they contain their own small
amplifier .

46. THE END…