The input and output units of a computer are used to interact with the outer world. there are a variety of input units that are used y computers. some of the devices are general-purpose means they are used by all computers. and the most commonly used unit of a computer is the keyboard. special units are magnetic ink character readers and scanners that can also be used to interact with the computer.

What are Input and output units?

An input unit is a unit used to give the input to the computer system. An output unit is a unit that is used to display information on the system that can easily read by the users.

Input and Output units in computer


The keyboard is the most common input unit used for manual data entry. we can use this device in all most all types of computers including a PC, workstations, or notebook computers. the arrangement of letters in the keyboard was standardized for mechanical typewriters. a keyboard consists of Letter keys, Digit keys, special character keys, nonprintable control keys, and function keys. when a key is pressed, the corresponding character is displayed on a display unit connected to it.

Display Unit

A display unit is like a video screen. whenever we press any button using the keyboard the corresponding character is displayed on the screen. a display unit is classified as an output unit because it displays the result of the computation. the data typed using a keyboard is immediately displayed on the screen of the display unit.


A mouse is a handheld device that has one or more buttons. the name mouse probably came as the wire connecting it to a display unit looks like a tail and the shape of the device resembles a mouse. a mouse is a locator and is used to move a pointing arrow or a cursor around the display screen. currently, the most commonly used mouse is the optical mouse.


A touchpad is a pointing device similar to a mouse that is used in laptop computers. it is a small pad situated below the keyboard. if a finger is placed on the pad, the capacitance changes as our body act as ground. the change in capacitance of the pad touched by the finger is translated to a pointer position on the display screen.

Touch screen

Some computers like tablet computers have not separate keyboards for giving inputs. but these computers use touch screens that also worked as same as a touchpad. when an icon is touched a program corresponding to it is invoked. the position is sensed by the printing on a liquid crystal display a set of transparent electrodes parallel to the x-axis.

Magnetic ink character recognition (MICR)

In this technology, human-readable characters are printed on the documents using a special magnetic link. a magnetic ink character reader can recognize such characters. for instance, the cheque number and branch code are pre-printed at the bottom using magnetic ink. and the amount written in the cheque is entered later by a clerk using a machine that prints the amount with magnetic ink.

Optical mark reader and recognition (OMR)

In this technology special, pre-printed forms are designed with boxes that can be marked with a dark pencil or ink. each box is annotated distinctly so that the user clearly understands his response when he darkens a box. such a document is read by a document reader which transcribes the marks into an electrical pulse which are transmitted to the computer.

Optical Character recognizer

This software takes the scanned text as input and covers it into its ASCII-coded equivalent. the main principle used by the OCR software is to compare each scanned letter with a sample set stored in the computer and find a match. this matching becomes easy if the font used is known to the OCR software and a uniform font is used.

Bar code

In this method, small bars of varying thickness and spacing are printed on packages, badges, and tags. that are read by optical readers and converted to electrical pulses. these codes have recently become popular, particularly among advertisers. the code consists of three distinct squares in the top two and the bottom left corner and a smaller square a little inside the bottom right corner. the rest of the square area has a large number of tiny squares which encode data. the QR code is read by a digital camera and a program is used to decode the contents.

E-ink display

It is primarily used to display e-books. this display's main advantage is that it does not consume any power while it displays a page. only when a new page is to be displayed power is consumed. another advantage is easy readability in bright light.


Printers are used to print the documents as hard copies. some fonts are already defined in the printers. when it gets the input as an image or any other input, it displays the corresponding image using the colors and default fonts.


This software is used to draw engineering drawings, such as building plans, machine parts, circuit diagrams, etc. special plotters to produce good quality drawings have been designed and are available in the market.