The document discusses various input and output devices for computers. It describes keyboards, mice, scanners, light pens, and microphones as common input devices. Keyboards convert pressed keys into electronic signals representing input, while mice allow cursor movement on screen using light sensors. Light pens detect screen light to select menu options. Microphones record sound as computer files. The document also outlines visual display units, plotters, printers, and speakers as major output devices, describing how printers can be either impact-based or non-impact and how speakers produce sound from computer audio.

2. Some input devices are :-
i. Keyboard
ii. Mouse
iii. Scanner
iv. Light pen
v. Microphone

3. Keyboard
It is the most commonly used input device. It
has various keys like numeric keys, alphabetic keys,
function keys, symbol keys, special keys like delete,
arrow keys. When a key is pressed an electric
signal exclusive for each key is generated which
passes to the control unit. So , the input signal is
converted into computer understandable code by
the keyboard itself.

4. Another very popular device is mouse. It is
about the size of human palm and rolls on a
small bearing and has one or more buttons
on the top. When a user rolls mouse on a flat
surface, the cursor moves accordingly on the
screen. Nowadays mouse is in great demand.
It uses the reflected light to sense the
direction of the movement.

6. It is a device for direct data entry. A special pen
which has photo cells in its tube is attached to the
monitor. When the pen is brought in contact with
the screen, it detects the light emitted by the
screen and this light activates the photocells.
These photocells when activated generate electric
pulses. Electric pulses send data to the computer
and it can detect which menu option has been
selected.

7. Microphone is a device which records voice or
sound and puts it in the computer in form of a file.
This file has as an extension .wav. Many laptops
and some desktop monitors have inbuilt
microphone in the form of a small hole in the
front, otherwise a microphone is easily available in
the market at a very low cost. Many microphones
come with a headset earphones too.

8. Some output devices are:-
i. Visual Display Unit(VDU)
ii. Plotters
iii. Printers
a).Impact printers
b).Non-impact printers
iv. Speakers

9. It is used to view the output generated by the
CPU in text or pictorial form. A VDU is similar to
a television screen and consists of a cathode ray
tube (CRT).
Some characteristics of VDUs are:-
• Display Colors
• Size
• Resolution

10. These are used to display graphical output. Flat
Bed Plotters use a fixed paper and a pen-holding
mechanism is allowed to move over it. Drum
plotters use a paper placed over a drum that rotates
back and forth to produce an up-down motion.
One or more pens containing same or different
inks are mounted horizontally and their movement
is controlled through a computer.

11. They are the most commonly used output
devices which produce a permanent copy of the
output on a paper called the hardcopy. The
digital copy of the documents stored in the
memory is called the softcopy. Two broad
categories of printers are :-
a).Impact printers
b).Non-impact printers

12. Printers in which the paper comes in direct
contact with the printer ribbon and printer
head are called impact printers.
Common Categories:-
• Dot matrix printers
• Daisy wheel printers

13. Printers where paper does not come in the
direct contact with the printer head are
called non-impact printers. These use
techniques like
thermal, electrostatic, laser, chemical or
inkjet technologies.
Common Categories:-
• Laser printer
• Inkjet printer

14. Speakers
They are also known as multimedia speakers and
add life to music, movies and games on PCs by
providing required sound effects. Speakers come
in various sizes, output quality and price range.
The speakers are equipped with low-power
internal amplifiers and normally have a plug in
connector lime green in color. Many VDUs have
built-in speakers with very basic configuration.
Mostly the external speakers are two plastic
boxes which have the volume and tone control
buttons.