Cit Notes for Reference

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computer science

1. I/O Devices1
2. Memory19
3. Central Processing Unit47
4. PC Hardware59
5. Database Concepts75
6. Review of C++90
7. Object Oriented Programming109
8. Polymorphism136
9. Inheritance144
10. Files167


Data are entered in to the computer system by means of an input device. The keyboard is one of the most commonly used input device. Other common one included are MICR, OCR, OMR, Digitizer, Joystick, trackball, light pen, mouse etc. There are also unusual input devices that respond to voice and touch. On touch sensitive screens, the user simply touches the location on the screen, where the description of the desired operation is displayed. The computer senses where the screen has been touched and performs the indicated operation.

The following are some functions performed by the input unit.

1. It accepts the list of instructions and data performed by the input unit. 2. It converts these instructions and data from the outside world. 3. It supplies the converted instructions and data to the computer system for further processing.

Key Board

It is the most common and familiar input device used. A keyboard typically has characters printed on the keys and each press of a key typically corresponds to a single written symbol. When a user presses a key, electric signals must be generated which will enable the computer (or other device) the switch in the housing are closed, and the two terminals at the output are effectively connected When the plunger is up( i.e., when the key is not pressed) the switch in the housing is open , and the terminals are not electrically connected. The most popular keyboard used today is the 101 keys QWERTY keyboard.

Keys in keyboard

To determine which key is pressed. This is called encoding. The encoding process is dependent on the mechanism used to make the individual keys in the keyboard.


The most direct method for encoding is based on the use of keyboard switches, which contain a switch similar to the push button switch used in many electric devices. When the plunger is depressed, the contacts of Enter/Return :used to alert your system that you have finished supplying the instructions. In word processing program, pressing Enter key begins a new paragraph.

Function key : Functions of these keys are expanded on software we used

Typewriter Keys :These keys are used to enter alphabets, punctuations etc.

Cursor controlling : These keys are used for moving the cursor to different positions on the screen. Cursor controlled keys include arrow keys, page up, page down, Home, End keys.

Combination Key : Ctrl, Alt, Shift are called combination keys because these keys are used with other keys. Functions of these keys depend on the software we use.

Esc : used to cancel the entry or operation.

Delete : used to delete characters in the current cursor position.

Caps Lock key : used to on/off caps lock facility.

Back space : It erases the character to the left and moves the cursor one position on back.

Numeric keypad : The rightmost part of the keyboard is called numeric keypad because it looks like keys of a calculator. All arithmetical operations are made by using these keys.

Various keyboards are –

1. Standard key boards such as 101 keys include alphabetic characters, punctuation symbols numbers and variety of function keys. 2. Multimedia keyboard with extra keys such as special keys for accessing music, web and other frequently used programs and features such as mute button, volume button, standby button etc.

Ergonomic keyboard

Now that virtually everybody in the workplace uses a keyboard to some degree, the stress that repetitive typing causes on the hands, wrist, and fingers has...
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