Keyboard: Keyboard is the most common input device.The data and instructions are input by typing on the keyboard. The message typed on the keyboard reaches the memory unit of a computer. It is connected to a computer via a cable. Apart from alphabet and numeral keys, it has other function keys for performing different functions.
Mouse: It is a pointing device. The mouse is rolled over the mouse pad, which in turn controls the movement of the cursor on the screen. You can click, double click or drag the mouse. Its sensor notifies the speed of its movements to the computer, which in turn moves the cursor/pointer on the screen.
Scanner: Scanners are used to enter information directly into the computer memory. This device works like a Xerox machine. The scanner converts any type of printed or written information including photographs into digital pulses, which can be manipulated by the computer.
Track Ball: Track ball is similar to the upside- down design of the mouse. The user moves the ball directly, while the device itself remains stationary. The user spins the ball in various directions to affect the screen movements.
Light Pen: This is an input device which is used to draw lines or figures on a computer screen. It is touched to the CRT screen where it can detect raster on the screen as it passes.
Optical Character Reader (OCR): It is a device which detects alpha numeric characters printed or written on a paper. The text which is to be scanned is illuminated by a low frequency light source. The light is absorbed by the dark areas but reflected from the bright areas. The reflected light is received by the photocells.
Barcode Reader: This device reads barcodes and converts them into electric pulses to be processed by a computer. A bar code is nothing but data coded in the form of light and dark bars.
Voice Input Systems: It converts spoken words to machine language form. A microphone is used to convert human speech into electric signals. The signal pattern is then transmitted to a computer when it is compared to a dictionary of patterns that have been previously placed in a storage unit of the computer. When a close match is found, the word is recognized.
Digital Camera: It converts graphics directly into digital form. An electronic chip is used in cameras, when light falls on the chip through the lens, it converts light waves into electrical waves.