PC Computer Hardware Input Devices Part 1

PC COMPUTER HARDWARE

INPUT DEVICES

Data and instruction must enter the computer system before any computation can be performed on the supplied data. This task is performed by the input unit that links the external environment with the computer system. An input device converts input data and instruction into suitable binary form which can be accepted by computer. The commonly used input device is keyboard. A number of input devices are there which do not required typing for inputting information e. i. mouse, light pen, joy stick track ball, touch screen etc. However regardless of their inputs all input devices must provide a computer with data that are transformed into the binary code that the primary memory of computer is designed to accept. This transformation is done by unit called input interfaces..

In short, the following functions are performed by input unit

• It accepts [or reads] the list of instructions and data from the outside world.
• It converts these instruction and data in computer acceptable form (electronic pulses).
• It supplies the converted instructions and data to the computer system for further processing
  

The input unit may be any one or combination of two or mare units out of following.

• Punched card
• Punched Paper Tape
• Keyboard
• Light pen
• Mouse
• Joy Stick
• Digitizer
• Voice recognition System
• Optical marker reader
• Optical Character reader
• Magnetic ink Character Recognition System

PUNCHED CARDS

This was earliest method of feeding data into computer. First punched card system was introduced by Dr. Hermann Hollerith in year 1887 for US census. The most popular design of punched chard was introduced by computer company IBM. The punch card is little longer and less broader than Indian Post Card, It contains total eighty column and twelve rows. Each column is meant for punching a pattern of square type holes for each character. The punching is done with the help of card punching machine which is very similar to a typewriter. When you press a key marked A, the card puncher will punch two holes as per code.

PUNCHED PAPER TAPE

A strip of paper 12.5 mm to 75mm wide and 90 to 300 m long was used for feeding data into computers in previous years.

The data is punched on these tapes with the help of a tape puncher using eight channel code or five channel 29 code . Corresponding to each character, a pattern of circular hole is generated according to certain code.


KEYBOARD

Each micro computer consists of a key board as input unit . In addition, the key board contains several command keys and function keys. Beneath each key . There is set of electrical contacts, which are closed when the key is pressed. By closing the electronic circuit, a signal (corresponding to character contained by key) is produced which is sensed by computer. This signal makes the character pressed to appear on the screen. Multi lingual key boards have been also devised.

Keyboards of special design are used for musical computer. In such key, piano type keys are provided through which any tune can be played . The standard IBM PC keyboard can be divided into three general areas:

• Typewriter area , having the standard set of alphabet letters and number keys.
• Function keys F1 through F12- which have different functions depending on the software in use. F1 is mostly used for getting help

Numeric keypad, having cursor control and number keys. Some on this pad have dual roles and the required number is obtained by either pressing along with shift key or by first pressing NUMLOCK key . The number keypad is used for entering large amount of numeric data.

GRAPHIC INPUT

Any information in the form drawing can be put into computer’s memory on visual display unit. The graphic pad has a magnetically sensitive surface that allows shapes to be drawn with the help of an electronic pen. The movement of pen is sensed by the electronic circuit below the pad which converts the movement signals into binary electrical pulses. These pulses travel into CPU of computer that displays the information on screen of VDU.


LIGHT PEN

Light pen is a device which enables us to write anything directly on the screen of computer. We can draw sketches and diagrams also. The light pen has got a tip which is very much sensitive to light. Actually it is a photosensitive detector. A bright spot of light known as raster spot moves in a orderly way across the back of computer‘s screen which alerts the tip of light pen.

MOUSE

A mouse is also a pointing device. It is held in one hand and moved across a flat surface. About the size of the normal cake of bath soap, it usually rolls on a small rubber ball and has two or three buttons on the top. When the user rolls the mouse across the flat surface the cursor on the screen moves in the direction of mouse movement, giving the user a sense of pointing at something on screen.

Positioning a cursor with a mouse is easier for non typists than pressing various key combinations. With proper software, a mouse can also be used to draw pictures on screen and edit text , as is done with software like Ventura, CorelDraw, etc. in DTP system.


JOYSTICK

A joystick is also used to move the cursor position on screen its function is similar to that of a mouse. Children can play with computers in a simple way by the use of joystick. While paying video games like SPACE- INVANDERS, user need to move space craft quickly across the screen. This can be done by pressing key on keyboard but it is neither convenient nor comfortable for small children to use the key board . This type of action can be better done with the help of joystick. As move the stick around in its socket the movements are translated into binary instructions with the help of electrical contacts.

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