Computer Hardware

We know hardware refers to physical, electrical, mechanical and electromechanical components of a computer. The Input unit is one, through which computer receives the information and send the processed output onto the output device. In this chapter we discuss the different types on input devices and output devices and their working procedure.


A keyboard is an input device used to enter data into a computer. The keyboard contains function keys, numeric keys and toggle keys (caps lock, num

lock, scroll lock) and so on. Some keyboard supports 1

00 and some support 104 keys.

A keyboard is used to enter data into a computer. The latest keyboard (Windows keyboard) is available with 104 keys. The keyboard contains function keys, numeric keys and toggle key (Caps lock, Num lock, Scroll lock) and so on.

It is the most widely used input device. it has keys similar to a typewriter to enter characters and other symbols. The function keys are used to activate a particular feature of software like invoking the help system, selecting a menu and so on.

There is a separate numeric keypad to enter

numeric keypad to enter numeric data. When a key is pressed the electric circuitry under the key will change which will be detected by the microproce

ssor and the binary code for the character is sent to the CPU. Some keyboards have a temporary memory or buffer to store the information typed a little ahead of the need of the computer.


A mouse is an input device used to select a command by moving it in any direction on a flat surface. It has two or three buttons to confirm the selection.

The software developed with graphical inter

face requires the mouse. The cursor is moved to the required icon or menu on the monitor and a button is pressed. The control is sent to the CPU t

o select the command corresponding to the icon or menu ite

m. The latest is the wireless mouse or remote mouse which works on transmission of infrared or radio waves are also available.

The mouse can also be used to open men

us, select text for editing, move objects on the screen and draw images or diagrams. The mechanical mouse uses a rubber-coated ball on

the underside. The movement of this ball sends electrical signals to the system unit which cause the cursor or pointer to move in a corresponding fa

shion. An optical mouse uses diodes to emit light onto a metal pad performing the same work but with great accuracy.


A peripheral input device used to assist in the

entry of data into a computer system. In desktop publishing, a scanner may be used to digitize artwork or photographs so that they can be merged with text. Scanners are used to scan a printed page

or an illustration. These data are then converted into bit patterns for processing storage or output. When an image is scanned, it is converted into light and d

ark picture elements or pixels. The scanned images are used for word processing and printing multiple copies. Scanners are also useful to scan fingerprints. The scanned fingerprints can be compared with another fingerprint to find probable match in investigative services. Photoelectric scanners are commonly

used in supermarkets to read barcodes.

Scanners are available in different sizes. A handheld

scanner is used to scan a few lines of text or a small photograph. A page scanner is used to scan a drawing or page.

The scanner is connected to the computer usin

g a cable and controlled by software.

Output devices:

Hard copy:

The data consisting of text or graphics that is obtained as printouts or microfilm using printers or plotters is known as hardcopy.

For example, the hardcopy of an engineering drawin

g is obtained using plotters. Some hardcopy devices include dot matrix printer, laser printer, inkjet printer , flatbed pen plotter and drum type inkjet plotter.

A combination of printing, scanning, copying and/or

faxing can also obtain a hardcopy. A hardcopy can be used for business correspondence and document

ation. A copier machine also comes under hardcopy devices.

Soft copy:

The data that is stored in a storage device such as floppy disk, hard disk, CD-ROM magnetic tape and so on is called softcopy.

The data in a softcopy may be modified using the relevant software. A few softcopy devices are monitor and floppy disk.


A printer is an output device used to print text o

r graphics on paper or on any other hardcopy medium which includes even microfilm. A permanent copy from the computer is produced using the printer. Printers are of two basic types impact and non-impact.

Impact and Non-impact printers:

Printers are categorized based on the physical c


ct of the print head with the paper to produce a text or an image. An impact printer is one where the print head will be in physical contact with the paper. In a non–impact printer, on the other hand the print head will have no physical contact with the paper

. The Dot matrix printer is considered as a Impac

t printer and Laser printer is considered as Non-impact printer.

The basic operations performed by a printer are:

1) Moving the paper to a given line.

2) Moving the print head along the line.

3) Generating the character or image.

4) Producing the character or image on the paper.

Dot Matrix Printer:

The most popular kind of printer for small computers is the dot matrix printer, which forms characters as arrays of dots. Dot matrix printers are compact, re

liable and relatively fast. This type of printer is an impact printer. The print head is the important hardware which produces the character using pins arranged in a matrix form. Normally a print head has 9 pins or 24 pins arranged in a matrix form. Combinations of pins strike an ink bed ribbon during the printing process. The print head moves in a line

and the pattern of dots required for each character is printed on the paper. After printing a line, the paper rolls to print the next line.

Dot matrix printers produce average quality prints and as generally used in business applications. They are used printing train number, seat number etc on a railway reservation ticket. The speed of printing in dot matrix printer in dot matrix is measured in ch

aracters per second (cps).

The advantages in this type of printer is carbon co

pies can be obtained as printing takes place by physical impact with the paper. It is less of cost and easy to maintain.

The disadvantage is average printing quality and printer ribbon printer ribbon needs to be changed frequently.

Laser Printer:

Laser printers are fastest type of non impact electrostatic printers. They produce high quality prints at high speeds. It operates like a copier machine. In these printers, the controlled beam of intense laser forms images on an electrically charged rotating drum. The drum is rotated near the fine black powder called the toner. These charged images which sticks to the paper due to pressure and heat. The toner consists of oppositely charged ink particles which stick to the drum in the places where the laser has charged.

The light beam strikes a multi-sided rotating mirror. As the mirror rotates, the side currently in the path of the light beam sweeps the beam across the surface of the drum. As the beam sweeps across the drum, the light is modulated and a single line is drawn after a line has been drawn, the next side of the mirror is in place and a new line is drawn below the previous line.

The quality of the printout is measured by the number of dots per inch (dpi). Since the dots are printed closely, the text or graphics appears very smooth and elegant. The speed is measured in number of pages printed per minute (PPM) which varies between 5 and 25.

The advantages are good quality printouts can be obtained for documentation and business applications. The printing is faster and easy to handle and maintain. The disadvantages are the price is high and higher print cost.

Inkjet printer:

An inkjet is a non impact printer. It sprays tiny drops of ink to form character and graphic images on paper. The text and graphics printed in an inkjet printer are technically similar to that of a dot matrix printer. These type of printers can also be used color printing. The black inkjet printer uses black cartridge filled with black ink whereas the color printer uses four color cartridges namely cyan (blue), magenta (red), yellow and black. These four colors are used in combination to generate any color in the visible spectrum.

The print heads move across the page by the control of software and spray the dots of ink with the required combination of colors. The printer sends electrical pulses to thin resistors at the base of firing chambers behind the nozzle. A thin layer of ink is heated by the resistor which in turn forms a vapour bubble and the expansion forces ink through the nozzle and onto the paper at a rate of about 6000 dots per second. The quality of the printout is equivalent to that of laser printouts. The speed of printing is slower than that of laser printers.

The advantages of this type printer are the cost is low; quality of printing is equivalent to that of laser printing, color printouts are cheaper easy to handle and maintain.

The disadvantages are the ink cartridges may get spoiled if unused for a long time. Some inkjet printers are very expensive.

There are two basic types of plotters: flat bed plotters and drum type plotters. Pen plotter is an example of a flatbed plotter. Laser plotter and inkjet plotter are commonly used drum type plotters.

A pen plotter has a surface where the paper or drawing sheet is properly fixed. It has a pen holder in a movable arm. Under the control of the computer the arm with the pen moves across the paper to draw the picture. A few pens are also placed in a row and the arm will pick the required color pen as per the instruction of the computer.

A drum type plotter uses a drum where the paper will be rolled. It has a print head/pen that moves like the print head in a printer. Drum type plotters are capable of producing longer, continous drawings. Drum type plotters that can produce color plots are available.

The disadvantages are these are expensive than printers. The cost of printing is high. Cost of maintenance is high. High skill of operation is required. Process time of printing is longer.