Notes and Study Materials

A computer is only useful when it is able to communicate with the external environment. When you work with the computer you feed your data and instructions through some devices to the computer. These devices are called Input devices. Similarly, computer after processing gives output through other devices called output devices.


I. Input Devices


Input devices are necessary to convert our information or data into a form which can be understood by the computer. A good input device should provide timely, accurate and useful data to the main memory of the computer for processing followings are the most useful input devices.





This is the standard input device attached to all computers. The layout of the keyboard is just like the traditional typewriter of the type QWERTY. It also contains some extra command keys and function keys. It contains a total of 101 to 104 keys. You have to press correct combination of keys to input data. The computer can recognize the electrical signals corresponding to the correct key combination and processing is done accordingly.


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The mouse is an input device which is used with your personal computer. It rolls on a small ball and has two or three buttons on the top. When you roll the mouse across a flat surface the screen censors the mouse in the direction of mouse movement. The cursor moves very fast with mouse giving you more freedom to work in any direction. It is easier and faster to move through a mouse.


3. Scanner:

The keyboard can input only text through keys provided in it. If we want to input a picture the keyboard cannot do that. The Scanner is an optical device that can input any graphical matter and display it back.


4. Magnetic Ink Character Recognition (MICR):

This is widely used by banks to process large volumes of cheques and drafts. Cheques are put inside the MICR. As they enter the reading unit the cheques pass through the magnetic field which causes the read head to recognize the character of the cheques.


5. Optical Mark Reader (OMR):

This technique is used when students have appeared in objective type tests and they had to mark their answer by darkening a square or circular space by pencil. These answer sheets are directly fed to a computer for grading where OMR is used.


6. Optical Character Recognition (OCR): 

This technique unites the direct reading of any printed character. Suppose you have a set of handwritten characters on a piece of paper. You put it, inside the scanner of the computer. This pattern is compared with a site of patterns stored inside the computer. Whichever pattern is matched is called a character read. Patterns that cannot be identified are rejected. OCRs are expensive though better the MICR.


7. Joy Stick:

This is one of the popular input devices, which is used for playing video games.


8. Touch Screen:

The Touch screen takes input as when a finger or object comes in contact with the screen, the light beam is broken, and the location of the breaking of a light beam is recorded, which acts as inputs.


9. Light Pen:

Light is a type of pointing device that is used to choose a displayed menu option on screen for a program. This pen contains a photocell placed in a small tube.


10. Voice Input Devices:

These devices are in the stage of experimenting and development, where various problems like speech should be independent of persons.


II. Output Devices




Output devices can adopt different shapes and styles, which are used to give the output of the processing of data. The output can be in any form i.e. typed, printed, sketched, visible, nonviable, audio, video etc. Output devices are those peripheral devices that allow a user to retrieve information from a computer. Any Output devices can be divided into two basic categories.

1. Hard Copy:

It is that form of output which can be read directly and immediately, stored to be read later. This output is on paper and which is permanent.


2. Soft Copy: It is the magnetic or audio form of output which is usually unreadable directly and which is not long-lasting.

I. Hard Copy Devices:

These are those devices, which produce a permanent record of data on media like paper. These are relatively slow in operation when compared to soft copy devices. Some of the popular devices are Printers, Plotters, and Photographic output devices.

1. Printers: Printers can be categorized into


Impact Printers
Non-impact Printers


Impact Printers

These are those types of printers which have direct mechanical contact between the head of the printers and paper. The impact printers are


a. Dot Matrix Printers:  


These Printers print characters as a combination of dots arranged in a 5 x 7 matrix. The speed of these printers varies from about 30 to 600 characters per second. The printing head of these printer contains a vertical array of pins, which fires the selected pins against carbon ribbon or linked surfac e while the head moves across the paper to form a pattern of dots representing characters. These printers can print characters in draft quality, standard quality as well near letter quality.

b. Daisy Wheel Printers:


This printer is a solid font type character printer. The printing arms of the printer head look like petals of the flower. This printer is very slow, it prints about 60-90 characters per second. The hub rotates continuously, rotating at high speed and hammer strikes the appropriate character in its position. This printer also acts as a bi-directional printer.

c. Line Printers: These printers prints the total line at a time, giving the name line printers. They can be print 1000- 5000 lines per minute

Non -Impact Printers:  

These printers print without any direct mechanical contact between the head of the printer and paper. These printers can be categorized into

a. Thermal Printers:


These Printers uses heat sensitive paper in dot matrix method, on which hot needles are pressed to form characters. These printers print slow and make a little noise. The disadvantage is that it is not possible to print multiple copies simultaneously.


b. Inkjet Printers:


These printers use a mechanism where it sprays the ink from tiny nozzles through an electric field that arranges charged particles ink into characters. The paper absorbs the ink and it dries instantaneously. It is capable to print about 500cps, expensive but faster and we can also have color printing, by using ink various colors.


c. Laser Printer:


This type of printers uses laser beams which charge the drum negatively, to which black toner powder which is positively charged is stuck. When the paper rolls by the drum, the toner powder is transferred to the paper. These printers are very fast, quality is very good and speed about is 15,000 to 20,000 lines per minute.


d. Electrographic Printer:


This printer writes on special paper using electricity. The paper is held between two electrodes. These printers can either use wet process or dry process. The speed of these printers is fairly high and is about 20,000 cps. These printers are very reliable as there are very less moving parts.


e. Electro Static Printer:-


This printer uses a mechanism, where static electricity is used to create impressions on special paper. The charges attract toner power to the charged spots, giving the print. These printers are very fast and are capable for plotting graphs etc. The speed is very high i.e up to 20,000 lines per minute.

2. Plotter:

A plotter is an output device similar to the printer but normally allows you to print larger images. Their use is common in the design and research sector.


These devices output is usually not visible directly but the output can be viewed with the help of computer where one can update, modify data etc. Some of the softcopy output devices are.


a. Visual Display Unit:


The most popular input/output device is the Visual Display Unit (VDU). It is also called the monitor. A Keyboard is used to input data and Monitor is used to display the input data and to receive a message from the computer. A monitor has its own box which is separated from the main computer system and is connected to the computer by a cable. In some systems, it is compact with the system unit. It can be color or monochrome.


b. Terminals:


It is a very popular interactive input-output unit. It can be divided into two types: hardcopy terminals and soft copy terminals. A hard copy terminal provides a printout on paper whereas soft copy terminals provide a visual copy on the monitor. A terminal when connected to a CPU sends instructions directly to the computer. Terminals are also classified as dumb terminals or intelligent terminals depending upon the work situation.

III. Speakers:

Most computers are sold with the capability to add a pair of speakers to your system unit. In fact, in some cases, the monitor may have speakers built directly into the unit. This enhances the value of educational and presentation products and can now be considered a standard PC component.


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