Input and Output Devices: Types, Examples and MCQs

Every computer runs on the input-process-output cycle, and the devices sitting at the two ends of that cycle are the most examinable part of computer hardware. An input device accepts data and instructions from the user and converts them into the binary form the processor can work with. An output device takes the processed result from the processor and presents it in a form a human can read, see or hear. Questions in SSC, banking and railway papers are almost always one-line recall: name the device, name its class, or name the work it does. This chapter fixes those pairs so that the marks are not lost to guesswork.

Input devices and what each one does

The keyboard is the standard text input device. Its usual layout is called QWERTY, after the first six letters of the top letter row, and it descends from the mechanical typewriter perfected by Christopher Latham Sholes. A standard enhanced keyboard carries 104 keys, and those keys fall into five families: alphanumeric keys, the numeric keypad, the function keys F1 to F12, the navigation or cursor keys, and the special or modifier keys such as Shift, Ctrl, Alt, Caps Lock and Esc. The mouse is a pointing device invented by Douglas Engelbart, who built the first wooden prototype at the Stanford Research Institute and patented it under the name X-Y position indicator for a display system. A trackball is a mouse turned upside down: the ball is rolled with the thumb while the body stays still, so it needs no desk space. A joystick moves a lever inside a socket and is used for games, simulators and machine control. A light pen is a pen-shaped, photo-sensitive device that selects an item by being touched to the screen itself, and a digitizer, also called a graphics tablet, converts a hand-drawn figure into digital form for design work. A microphone, a web camera and a fingerprint reader are input devices too, because each of them feeds fresh data into the machine.

Scanning and recognition devices

A whole family of input devices reads marks, characters and codes instead of keystrokes, and examiners test the full forms and the uses of these devices more often than anything else in the chapter.

MICR deserves a second look because banking papers ask about it every year. The characters printed along the bottom of a cheque are set in magnetic ink in the E-13B font, and the reader picks them up from their magnetic signal, so the cheque is read correctly even when it is folded, stamped or soiled. The difference between the other two is worth one clean sentence each: OMR only detects whether a mark is present in a given position and cannot read what is written, while OCR recognises the shapes of the characters themselves and hands back text that can be edited.

Output devices: soft copy and hard copy

Output shown on a screen is called soft copy; output printed on paper is called hard copy. The monitor, also known as the Visual Display Unit or VDU, gives soft copy. The smallest element of the picture on it is a pixel, short for picture element, and the sharpness of the display depends on its resolution and on the dot pitch, the distance between two neighbouring dots of the same colour, where a smaller value means a sharper picture. The old CRT monitor used a cathode ray tube and was bulky; LCD and LED panels replaced it because they are flat, lighter and far more economical in power. A projector, a speaker, a headphone and a Braille embosser are output devices as well.

Printers and plotters

Printers are divided by one simple test: does the print head strike the paper or not. Impact printers such as the dot matrix, the daisy wheel and the drum and chain line printers strike an inked ribbon against the paper. They are noisy and slow, but they can take carbon copies at one pass, which is why counters that issue duplicate receipts used them for years. Non-impact printers never touch the paper. An inkjet sprays very fine droplets of liquid ink; a laser printer uses a laser beam, a photosensitive drum, dry powder toner and heat, and because it composes and prints one full page at a time it is called a page printer; a thermal printer heats chemically treated paper and is the machine inside billing counters and cash dispensers. Print quality is measured in DPI, dots per inch. Speed is measured in CPS, characters per second, for character printers, in LPM, lines per minute, for line printers, and in PPM, pages per minute, for page printers. A plotter is a pen-based output device that draws continuous lines rather than dots, which makes it the right machine for maps, architectural drawings and engineering design output; the drum plotter and the flatbed plotter are its two standard types.

Devices that work both ways

A short list, and a favourite of paper setters. A touchscreen takes a finger tap as input and displays the result as output on the same surface. A modem, whose name comes from modulator-demodulator, converts the digital signal of the computer into an analogue signal for the line and converts the incoming analogue signal back again. A network interface card, a headset that carries a microphone and an earphone together, and storage media such as the hard disk, the pen drive and a rewritable disc all carry data in both directions. Fix the exceptions in memory: a plotter and a monitor are output only, a scanner and a light pen are input only, and a hard disk is counted as both.