1. Input and output devices
1. Introduction
1.1 Definition:
A computer is an electronic machine that
1) takes in data and instructions (input)
2) works with the data (processing)
3) puts out information (output)
or
“General purpose machine, commonly consisting of digital circuitry, that accepts (inputs),
stores, manipulates, and generates (outputs) data as numbers, text, graphics, voice, video files,
or electrical signals, in accordance with instructions called a program.”
Computers are not very intelligent devices, but they handle instructions flawlessly and
fast. They must follow explicit directions from both the user and computer programmer.
Computers are really nothing more than a very powerful calculator with some great
accessories. Applications like word processing and games are just a very complex math
problem.
1.2Software and Hardware
If you use a player piano as an analogy, the piano can be thought of as the hardware and the
roll of music as the software.
The software a series of very simple computer instructions carefully organized to complete
complex tasks. These instructions are written in programming languages (like BASIC, PASCAL,
C...) to help simplify the development of applications.
The hardware is what sits on your desk and executes the software instructions. The player
piano is useless unless the roll of music has been written correctly.
1.3Hardware Components
Input Devices -- "How to tell it what to do"
- A keyboard and mouse are the standard way to interact with the computer. Other devices
include joysticks and game pads used primarly for games.
Output Devices -- "How it shows you what it is doing"

2. - The monitor (the screen) is how the computer sends information back to you, whether it be
surfing the web or writing a memo. A printer is also an output device.
Storage Devices -- "How it saves data and programs"
- Hard disk drives are an internal, higher capacity drive which also stores the operating system
which runs when you power on the computer.
2. Input devices
An input device is any device that provides input to a computer. There are dozens of possible
input devices, but the two most common ones are a keyboard and mouse. Every key you press
on the keyboard and every movement or click you make with the mouse sends a specific input
signal to the computer. These commands allow you to open programs, type messages, drag
objects, and perform many other functions on your computer.
Since the job of a computer is primarily to process input, computers are pretty useless without
input devices. Just imagine how much fun you would have using your computer without a
keyboard or mouse. Not very
much. Therefore, input devices are a vital part of every computer system. There are many
forms of input devices such as:
2.1 Keyboard
The keyboard is a way to input letters or numbers into different applications or programs. A
keyboard also has special keys that help operate the computer.
2.2 Mouse
The mouse is used to open and close files, navigate web sites, and click on a lot of commands
(to tell the computer what to do) when using different applications.
2.3 Joystick
A joystick is used to move the cursor from place to place, and to click on various items in
programs. A joystick is used mostly for computer games.
2.4 Track ball
A trackball is a pointing device consisting of a ball held by a socket containing sensors to detect
a rotation of the ball about two axes—like an upside-down mouse with an exposed protruding
ball.
2.5 Touch pad
A touchpad (or trackpad) is a pointing device featuring a tactile sensor, a specialized surface
that can translate the motion and position of a user's fingers to a relative position on screen.

3. They are a common feature of laptop computers and also used as a substitute for a computer
mouse where desk space is scarce.
2.6 Light pen
It is a pen shaped device used to select objects on a display screen. It is quite like the
mouse (in its functionality) but uses a light pen to move the pointer and select any
object on the screen by pointing to the object.
2.7 Microphone
A microphone is used to record sound. The sound is then saved as a sound file on the
computer.
2.8 Digital camera
A digital camera can be used to take pictures. It can be hooked up to a computer to transfer
the pictures from the camera to the computer. Some digital cameras hold a floppy disk, and
the floppy disk can be taken out of the camera and put directly into the computer.
2.9 Scanner
A scanner is used to copy pictures or other things and save them as files on the computer.
3. Output devices
Any device that outputs information from a computer is called, not surprisingly, an
output device. Since most information from a computer is output in either a visual or auditory
format, the most common output devices are the moniter and speakers. These two devices
provide instant feedback to the user's input, such as displaying characters as they are typed or
playing a song selected from a playlist.
While monitors and speakers are the most common output devices, there are many others.
Some examples include headphones, printers, projectors, lighting control systems, audio
recording devices, and robotic machines. A computer without an output device connected to it
is pretty useless, since the output is what we interact with. Anyone who has ever had a monitor
or printer stop working knows just how true this is. Of course, it is also important to be able to
send information to the computer, which requires an input device.
3.1 CRT Monitor
Monitor is an output device that resembles the television screen and uses a Cathode
Ray Tube (CRT) to display information. The monitor is associated with a keyboard
for manual input of characters and displays the information as it is keyed in. It also
displays the program or application output. Like the television, monitors are also
available in different sizes.

4. 3.2 Flat pannel monitor
encompass a growing number of electronic visual display technologies. They are much lighter
and thinner than traditional television sets and video displays that use cathode ray tubes
(CRTs), and are usually less than 100 mm (4 in) thick. They are thin and light. They provide
better linearity and higher resolution.
3.3 Printer
Printers are used to produce paper (commonly known as hardcopy) output. Based on
the technology used, they can be classified as Impact or Non-impact printers.
Impact printers use the typewriting printing mechanism wherein a hammer strikes
the paper through a ribbon in order to produce output. Dot-matrix and Character
printers fall under this category.
3.4 Plotter
Plotters are used to print graphical output on paper. It interprets computer commands
and makes line drawings on paper using multicolored automated pens. It is capable of
producing graphs, drawings, charts, maps etc.
3.5 Speaker and headset
The Audio output is the ability of the computer to output sound. Two components are
needed: Sound card – Plays contents of digitized recordings, Speakers – Attached to
sound card.
3.6 Digital light projector
Digital Light Processing (DLP) is a trademark owned by Texas Instruments, representing a
technology used in some TVs and video projectors. It is also one of the leading technologies
used in digital cinema projection. These rear-projection technologies compete against LCD and
plasma flat panel displays in the HDTV market