Input and output devices of computer

Input and output devices enable computer to interact with the external world. User Can enter data and instructions into the computer with the help of input devices. Whereas After processing the data, sends the results back to the output devices. The input can In variety of forms e.g. text, image, voice etc. Similarly output may be required in Forms depending upon the user’s requirements. That’s why a number of different Input and output devices are available.

Input Devices

The devices which are used to enter data and instructions into the computer are called input


The most commonly used input devices are:

  • Keyboard
  • Mouse
  • Microphone etc.

Before data processing, data and instructions must be entered into the computer

Some input device. The input device converts data and instructions into a form that a

Can process. The computer can process millions of instructions in a second and

Gives output in the form of information. The figure 3.1 shows the different categories

Of input devices.




Pointing devices → mouse-joystick

Scanning devices

Voice- devices

Digital camera



Keyboard is the standard input device used to enter textual data into the computer.

The layout of keyboard is just like the traditional typewriter. But it contains some extra

Command keys and function keys. Among the most popular keyboard layout are QWERTY

And Dvorak. The layout refers to the arrangement of keys on the keyboard. A typical

Keyboard can have 101 to 104 keys.


The keys on computer keyboards are often classified as follows:

  • Alphanumeric keys: Alphabets and numbers.
  • Numeric keys: Numbers and mathematical operators.
  • Function keys: key for special functions ( Fl, F2, F3  F12).
  • Cursor control keys: keys that move the cursor (Up, Down, Left, Right).

Alphanumeric Keys

These keys are used to enter alphabets, numbers and other special characters into the

Computer. Position of the keys is similar to that of a typical type writer. The keys are used

To input the following

  • Alphabet Keys; these consist of keys A to Z having both upper case and lower casf

Letters. The arrangement of alphabets on keyboard is as shown in figure 3.3. This

Arrangement is known as QWERTY layout.



Number keys: These consist of number keys starting from 0 to 9.

Special characters keys: These consist of punctuation keys, special characters, and Space bar.

Numeric Keys

These keys are used to input numbers into the computer. The layout of these keys is

To that of a typewriter. Along with the number keys it also contains keys for

Mathematical operations i.e., plus, minus, multiply, divide.

Function keys

Function keys are used to perform different functions depending upon the application

Or program that is executing. These keys provide shortcuts for doing routine tasks on a computer.


Most computer keyboards have a row of Function keys at the top of the keyboard.

Keys are marked from FL to F12. Many programs, including most of Microsoft’s

Products, support use of the function keys. The function keys are frequently used in

With other keys such as the CTRL key, the ALT key, and the SHIFT key. This

In a large number of possible keyboard shortcuts.

Cursor Control Keys

Cursor is used to represent the position where the keyboard’s input will be placed.

These four arrow keys are used for moving the cursor from its current position to right, left, up, or

Down. Moving these cursor keys does not change or delete any characters on the screen.

Are also used for screen navigation. The function of some of the other important keys is


ENTER KEY: Used to enter commands or to move the cursor to the beginning of

The next line. This is sometimes labeled as Return instead of Enter.

ESC KEY: Short for Escape, this key is used to send special codes to devices and to

Exit (or escape) from programs and tasks.

DELETE KEY: Deletes the character at the current cursor position and the one at

Right of the cursor position. Also used to delete the selected object, but it does not

Move the cursor.

CAPS LOCK KEY: A toggle key that, when activated, causes all alphabetic

Characters to be uppercase.

END KEY: Moves the cursor to the end of the line, the end of the page, or the end of

The file depending where the cursor is located on the page and on which program


CTRL KEY: Short for Control, this key is used in combination with other keys

Produce special characters. The meaning of each control character depends on w

Program is running.

ALT KEY: Short for Alternate, this key is used in combination with other keys

Produce special characters.

TAB: This key enables the cursor to jump a couple of spaces to the right on the

Screen. To jump the equivalent spaces to the left, Shift-Tab keys should be press


BACKSPACE KEY: Deletes the character present at the left of the cursor and

Moves the cursor to that position.

PAGE UP and PAGE DOWN: This is used to move the cursor up or down

Certain fixed number of lines usually one page at a time. This is often abbreviated

Pg Up and Pg Dn.

HOME: Moves the cursor to the left corner of the line or to the beginning of the

Page or file depending where the cursor is and on which program is running.

INSERT: In insert mode, all characters typed are placed at the cursor position (or

The right of the insertion point). With each new insertion, characters to the right of the



Cursor are pushed to the right of the insertion point to make room for the new

Characters. If insert mode is turned off, typing then overwrites existing characters

Instead of inserting the new ones before the old ones. This is often called overwrite

Mode. Most PC keyboards have an INSERT key that lets you switch back and forth

Between insert and overwrite mode.

Space Bar: This key moves the cursor one space to the right every time you press key. \



A mouse is an input device that rolls around on a flat surface and controls the pointer

On a display screen. The pointer is an on-screen object — usually an arrow — that is used to

Text; access menus; and interact with programs, files or data that appear on screen. As

You move the mouse, the pointer on the display screen moves in the same direction. A typical

Mouse has two buttons, which perform different functions depending on what application is

Some mouses also include a scroll wheel for scrolling through long documents.


Optical mouse is getting popular nowadays; instead of having a roller ball it uses

‘It pressed reflection to control the movement of pointer on the screen.

Mouse events:

Mouse event refers to the activity that can be performed by using the mouse. A typical

Mouse can perform the following events:


  • Left Click
  • Right Click
  • Drag

Left Click is used to select a graphical object such as a file icon and a piece of text in a

Document etc., or to press a button such as the start button and closing, opening or

Minimizing a window etc.


Right Click is used to view the properties

Of an object such as file, folder, desktop etc.


Drag event triggers when you keep on Pressing the left mouse button while

Moving the mouse. This event is used to Select more than one items at a time or-to

Drop an object into another application.



A Trackball is a pointing device that works like a mouse. Trackball contains a

Exposed on its surface. To move the pointer on the screen, you roll the ball with your thumb

Fingers, or the palm of your hand. There are usually one to three buttons next to the ball,

Which you use just like mouse buttons. The Advantage of trackballs over mouse is that the trackball is stationary so it does not require much space for use: in addition, you can place a trackball on any type of surface. For both these reasons, trackballs are popular Pointing-devices for portable computers.


Joystick is an input device used for games, Computer aided designs or simulations. It is like a lever that moves in all directions and Controls the movement of a pointer or some other display symbol. A joystick similar to a mouse, except at with -a Cursor stops moving as soon as you stop

In the-direction. The joystick is pointing. To stop the pointer, You must return the joystick to its neutral

Position. Most joysticks include two buttons Called triggers.



A scanner is an input device which is capable of reading the image present on a piece

Transferring the information into a computer where a program can store and inter pert

It. This information is in the form of a graphic image or picture and not in the Text. Even if the paper contains text but a picture of text. Optical character

Information transferred is not text. Recognition (OCR) software is necessary to read this image and convert it to actual text data and this software varies widely in its ability to do so. Scanners range from

(2 color) scanners to flatbed. And color scanners capable of a whole page at once and costing

Several thousand and rupees.


A Microphone is an input device used to digitally record audio data, such as the

Voice. It can be plugged into a Computer recorder. Many productivity

Applications can accept input via a Microphone, enabling the user to dictate text or issue Commands orally. Software in the computer convert the sound impulses into digital form. It is then stored in memory and processed when required.




A voice-recognition system, using a microphone as an input device, converts a person’s

Speech into digital data by comparing the electrical patterns produced by the

Speaker’s voice with a set of prerecorded patterns stored in the computer.

(Voice Recognition allows a user to use his voice as input. Voice recognition may be used to dictate text to the computer or to give commands to the computer such as opening

Application programs, pulling down menus, or saving work.

Older voice recognition applications require each word to be separated by a distinct

This allows the machine to determine where one word begins and the next stops. This

Of dictation is called discrete speech. Many people prefer these systems to the newer

Continuous speech.

Light pen

Light pen is a light-sensitive input device shaped like a pen. It is used to draw on the computer screen

Or to make menu selection. As the tip of the light pen makes contact with the


Screen, it sends a signal back to the computer containing the x-y coordinates of the

Light pens can be used on any size screen.

Light pens give the user the full range of mouse capabilities, without the use of any

Horizontal surface. Users can interact more with the application, using options such as drag

And drop, or highlighting. Pens offer more active and accurate interaction between the users

And the computer system.


 Digital Camera

Digital camera is a device that stores images digitally in its memory rather recording

Them on film. Once a picture has been taken, it can be downloaded to a computer system, and

Then manipulated with a graphics program and printed. Digital photos are limited by the

Amount of memory in the camera and by the quality of the final output device.


The big advantage of digital cameras is that making photos is both inexpensive

Fast because there is no film processing involved.

Disk Drive

A disk drive is a machine that reads data from and writes data onto a disk. Disk drive

Rotates the disk with precise timing has one or more read/write heads that read and write


Data is read by the read/write head and transferred to the computer’s main memory

Processing. There are different types of disk drives for different types of disks e.g.

Disk drive (HDD) reads and writes hard disks, and a floppy disk drive (FDD) accesses

Floppy disks, and an optical disk drive reads optical disk. Disk drives can be either internal

(Housed within the computer) or external (housed in a separate box that connects to the computer).

Output Devices

The devices which are used to receive data and information from the computer are.

Output devices

The most commonly used output devices are:

  • Monitor
  • Printer
  • Speaker etc.

Before goitvint0Aietails going into details of output devices it is necessary to discuss two basic concepts related to input/output devices i.e. hard copy and soft copy. An electronic version of a documents stored (normally as a file ) on a storage device is called document (on a paper ) is called hard copy . Here is a brief discussion on commonly used output devices.

                                                                                                                                      Remember that:

There are some devices

Which act as both input

And output devices e.g.

                                              image                                                                                      Touch screen, hard disk

Drive, floppy disk drive



The monitor is the most commonly used output device on personal computers (PCs).

Also called a display or a screen. You look at your monitor whether you are typing,

Commands, surfing the Internet, or even listening to music. The quality of the image

The screen depends upon many factors. Resolution is one of the factors affecting the

Quality of the monitor. The resolution of a monitor refers to the number of pixels on the

Screen, expressed as a matrix.

All the monitors can be categorized by the way they display colors. These are

Monochrome monitors and color monitors. Monochrome monitors can display only one color

As green, amber or white) against a contrasting background, which is usually black.

2ese monitors can display text only and are not used for displaying graphics. Color monitors

Display combinations of red, green and blue colors. These three are the basic colors and their

Combination can display a full range of colors.



There are two basic types of monitors. These are

  • CRT (cathode rays tube) monitor are
  • Flat panel monitor


A CRT monitor consists of a phosphorus coated screen; there are three guns

On its back. Screen’s phosphor coating is organized into a grid of dots. The smallest

Number of phosphor dots that the gun can focus on is called a pixel or picture element.


The three electron guns emit beams of three different colors i.e. red, green and

In color monitors each pixel include three phosphors — red, green, and blue — arrange:

Triangle. When the beams of each of these guns are combined and focused on a pixel, the

Phosphors lights up. The monitor can Display different colors by combining

Various intensities of the three beams. A CRT monitor contains a shadow Mask, which is a fine mesh made up of

Metal, fitted to the shape and- size of the

Screen. The holes in the shadow mask’s

Mesh are used to align the electron beams,

To ensure that they strike precisely the

Correct phosphor dot. In most shadow

Masks, these holes are arranged in triangle.



Flat panel monitors are usually used in portable computers and laptops because of

Their small size. They are expensive to manufacture and don’t provide the high quality and

Bright colors that CRT technology provides. There are several types of flat-panel monitors

But the most common is liquid crystal display (LCD) monitor.

LCD monitors create images with a

Special kind of liquid crystal that is normally transparent but becomes opaque when Charged with electricity. If you have a handheld calculator or a digital watch, it probably uses a liquid crystal display.



The quality of the images that a monitor can display is defined as much by the video

Controller as by the monitor itself. Video controller is an intermediary device between the

CPU and the monitor, It contains memory and circuitry necessary to send information to the

Monitor for display on screen. The resolution of the monitor is actually determine by the

Video controller. Not by the monitor e.g. Video Graphic Array (VGA) has resolution

640 X 480 pixels. Super Video Array (S VGA) has resolution 1024×768 etc.


A printer is a device that produce Hardcopy on the paper. Printers are common used in businesses

To get the documents printed on paper. Depending upon the printed mechanism used. Printers fall into two categories i.e.

  • Impact printers
  • Non-impact printers






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