Input and Output Devices.



Input device

Devices used to provide data and instructions to the computer are called Input devices. Some important input devices are

Key board, Mouse, Scanner, MICR, Web camera, Microphone etc.


1. Keyboard: The Key board is used for typing text into the computer. It is also known as standard Input device. A computer keyboard is similar to that of a type writer with additional keys. The most commonly available computer keyboard has 104 keys.


There are different types of keys on the keyboard. The keys are categorized as:

• Alphanumeric keys, including letters & numbers.

• Punctuation keys, such as colon (:), semicolon (;) Question mark (?), Single & double quotes (‗,‖)

• Special keys such as arrow keys, control keys, function keys (F1 to F12), HOME, END etc.


2. Mouse: It is a device that controls the movement of the cursor on a monitor. A mouse will have 2 buttons on its top.
The left button is the most frequently used button. There will be a wheel between the left and right buttons. This wheel enables us to smoothly scroll through screens of information.
As we move the mouse, the pointer on the monitor moves in the same direction.


Optical mouse is another advanced pointing device that uses a light emitting component instead of the mouse ball. Mouse cannot be used for entering the data. It is only useful to select the options on the screen.


3. Scanner: It is an input device that can read text or illustrations printed on paper and translate into digital form.
The main advantage of these scanners is that the data need not be entered separately resulting in saving lot of time.


Scanners are of two types:

optical scanners


i) Optical scanners:
a. Optical character Recognition (OCR): In this, characters are read with the help of a light. This is used in office atomization, documentation in library etc.

b. Optical mark recognition (OMR): It is a technology where an OMR device senses the presence or absence of a mark such as a pencil mark. OMR is used in tests such as aptitude tests.

c. Optical barcode recognition (OBCR): Barcode readers are photoelectric scanners that read the bar codes or vertical zebra striped marks printed on product containers. This is used in super markets, book shops etc.

ii) MICR:
This is widely used in banks to process the cheques.
This allows the computer to recognize characters printed using magnetic ink.


4. Magnetic Ink Character Recognition (MICR): It is a character recognition technology used primarily by the banking industry to facilitate the processing of the cheques. MICR characters (cheque No., Acc.No.etc) are printed in special ink usually containing iron oxide.

When a document that contains the ink needs to be read, it passes through a machine which magnetizes the ink and there will be a reader sorter unit which translates the magnetic information into characters.
MICR provides a secure, high speed of scanning and processing information.
It scans about 2600 cheques/min.


Output devices


Any device that is capable of representing information on a computer is called an Output device.
Output devices receive information from the CPU and present it to the user in the desired form. Some important Output devices are: Monitor, Printer


1. Terminal/Monitor: It is similar to TV screen- either a monochrome (black & white) or colour – and it displays the output.
It is also referred as Visual Display Unit (VDU). Several types of monitors are in use.

Some of them are Colour Graphic Adapter (CGA), Enhanced Graphics Adaptor (EGA), Video Graphics Adapter (VGA) and Super Video Graphics Adapter (SVGA).




The screen sizes differ from system to system. The standard size is 24 lines by 80 characters. Most systems have provision for scrolling which helps in moving the text vertically or horizontally on the screen.


2. Printer: A printer is used to transfer data from a computer onto paper. The paper copy obtained from a printer is often referred as ―printout‖.


The different printers and their speeds are as follows:


S/No Type Mode of Printing Speed
1 Dot – Matrix printer Prints the character in dotted pattern through printer ribbon using either 24 pin or 9 pin 200/300 to 700 CPS
2 Ink Jet printer Work by spraying ionized ink 2 Slow, 90 CPS
3 Laser printer Also called page printer. Uses laser beam to produce an image. 6 to 12 PPM
4 Line printer Prints lines at a time instead of single characters. 300 to 600 LPM
5 Plotter Produces drawings or graphs through pens which are filled with different colours.

(CPS : Characters Per Second;
PPM: Pages Per Minutes;
LPM: Lines Per Minute)


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