The
computer will be of no use unless it is able to communicate with the outside
world. Input/Output devices are required for users to communicate with the
computer. In simple terms, input devices bring information INTO the computer
and output devices bring information OUT of a computer system. These
input/output devices are also known as peripherals since they surround the CPU
and memory of a computer system.
Some
commonly used Input/Output devices are listed in table below.
Input Devices
(a)
Keyboard
It is a text base input
device that allows the user to input alphabets, numbers and other
characters. It consists
of a set of keys mounted on a board.
Alphanumeric
Keypad
It consists of keys for English
alphabets, 0 to 9 numbers, and special characters like + −
/ * ( ) etc.
Function
Keys
There
are twelve function keys labeled F1, F2, F3… F12. The functions assigned to
these keys differ from one software package to another. These keys are also
user programmable keys.
Special-function
Keys
These
keys have special functions assigned to them and can be used only for those
specific purposes.
Functions of some of the important keys are defined below.
- Enter
It
is similar to the ‘return’ key of the typewriter and is used to execute a
command or program.
- Space bar
It is used to
enter a space at the current cursor location.
- Backspace
This
key is used to move the cursor one position to the left and also delete the
character in that position.
- Delete
It is used to
delete the character at the cursor position.
- Insert
Insert key is
used to toggle between insert and overwrite mode during data entry.
- Shift
This
key is used to type capital letters when pressed along with an alphabet key.
Also used to type the special characters located on the upper-side of a key
that has two characters defined on the same key.
- Caps Lock
Cap
Lock is used to toggle between the capital lock features. When ‘on’, it locks
the alphanumeric keypad for capital letters input only.
- Tab
Tab
is used to move the cursor to the next tab position defined in the document.
Also, it is used to insert indentation into a document.
- Ctrl
Control
key is used in conjunction with other keys to provide additional functionality
on the keyboard.
- Alt
Also
like the control key, Alt key is always used in combination with other keys to
perform specific tasks.
- Esc
This
key is usually used to negate a command. Also used to cancel or abort executing
programs.
- Numeric Keypad
Numeric
keypad is located on the right side of the keyboard and consists of keys having
numbers (0 to 9) and mathematical operators (+ − * /) defined on
them. This keypad is provided to support quick entry for numeric data.
- Cursor Movement Keys
These
are arrow keys and are used to move the cursor in the direction indicated by
the arrow (up, down, left, right).
(b) Mouse
The
mouse is a small device used to point to a particular place on the screen and
select in order to perform one or more actions. It can be used to select menu
commands, size windows, start programs etc.
The
most conventional kind of mouse has two buttons on top: the left one being used
most frequently.
Mouse Actions
- Left Click : Used to select an item.
- Double Click : Used to start a program or open a file.
- Right Click : Usually used to display a set of commands.
Drag
and Drop : It allows you to select and move an item from one location to
another. To achieve this place the cursor over an item on the screen, click the
left mouse button and while holding the button down move the cursor to where
you want to place the item, and then release it.
(c)
Joystick
The
joystick is a vertical stick which moves the graphic cursor in a direction the
stick is moved. It typically has a button on top that is used to select the
option pointed by the cursor.
Joystick is used as an input device primarily
used with video games, training simulators and controlling robots.
(d)Scanner
Scanner
is an input device used for direct data entry from the source document into the
computer system. It converts the document image into digital form so that it
can be fed into the computer.
(e) Bar codes
Reader
A
bar code is a set of lines of different thicknesses that represent a number.
Bar Code Readers are used to input data from bar codes.
Most products in shops
have bar codes on them.Bar code readers work by shining a beam of light on the
lines that make up the bar code and detecting the amount of light that is
reflected back.
(f) 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.
Users
of Computer Aided Design (CAD) applications commonly use the light pens to
directly draw on screen.
(g)Digital
camera
A
digital camera can store many more pictures than an ordinary camera. Pictures
taken using a digital camera are stored inside its memory and can be
transferred to a computer by connecting the camera to it. A digital camera
takes pictures by converting the light passing through the lens at the front
into a digital image.
(h) The Speech
Input Device
The
“Microphones - Speech Recognition” is a speech Input device. To operate it we
require using a microphone to talk to the computer. Also we need to add a sound
card to the computer. The Sound card digitizes audio input into 0/1s .A speech
recognition program can process the input and convert it into
machine-recognized commands or input.
Output Devices
(a)
Monitor
Monitor
is an output device that resembles the television screen and uses a Cathode Ray
Tube (CRT) to display information.
It also displays the program or application output. Like the television,
monitors are also available in different sizes.
Now a days we use Liquid Crystal Display (LCD). LCD are smaller and lighter than cathode ray tube monitors, they consumed less power then CRT Monitors.
(b) 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.
Non-impact
printers do not touch the paper while printing. They use chemical, heat or
electrical signals to etch the symbols on paper. Inkjet, Deskjet, Laser,
Thermal printers fall under this category of printers.
(c) 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.
Computer
Aided Engineering (CAE) applications like CAD (Computer Aided Design) and CAM
(Computer Aided Manufacturing) are typical usage areas for plotters.
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