Automatic Input and Output Devices

I. A modem links a computer to a network and enables it to communicate with other computers linked to the same network. It functions as both an input and an output device. A modem converts computer data to signals that can be sent and received over standard telephone lines. It also converts signals it receives over telephone lines back to computer data. A modem may be either an internal device or a peripheral. Many computers are sold with a modem already installed.

A scanner is a peripheral that uses light to digitize photographs and other illustrations. Publishers are major users of scanners, but scanners also popular with home computer users. A scanner equipped with optical character recognition (OCR) software can translate the scanned image of text into individually encoded characters.

There are flatbed and hand-held scanners. Flatbed scanners are the most widely used. A flatbed scanner has a glass surface at least as large as a standard sheet of paper. The user lays the material to be scanned face down on the glass. The device scans the image through the glass and digitizes it. A user holds a hand scanner in one hand and rolls it over the material to be scanned. Most hand scanners are narrow, and so they must be passed over a page section by section.

Laser devices that read bar codes at checkout counters in stores are also types of scanners, but they do not digitize images. They instead send coded numerical information to a store’s main computer.

A microphone translates sound into electric current, which a sound card in the computer then digitizes. Digitized sound information may be sent over a network from one computer to another. It can then be converted back into sound by the sound card of the receiving computer.

II. Output devices display the work done by the computer. These devices include monitors, printers, plotters, and speakers.

Monitors have a screen much like a television screen. Modern monitors offer millions of color combinations. The most common type of monitor used with a desktop machine is a cathode-ray tube (CRT).

There is also a liquid crystal display (LCD), an electro-optical device used to display digits, characters or images. It is commonly used in digital watches, calculators, and portable computers.

Printers output information on paper. There are three major types: (1) laser, (2) inkjet, and (3) dot matrix.

Laser printer is a high-resolution printer for computer output that prints an image formed by a laser.

Inkjet printer sprays ink onto paper using a tiny nozzle that quickly moves back and forth to form text and illustrations. Color inkjet printers have separate ink tanks for each primary color and one for the black color.

Dot-matrix printer uses tiny pins that strike and inked ribbon positioned in front of the paper. Laser and inkjet printers have largely replaced dot-matrix printers.

Plotters use pens to create drawings, diagrams, and graphs on paper or clear plastic. Architects often use plotters to prepare large blueprints and plans.

Speakers play sound files. Desktop computers usually come with separate speakers that can produce high-quality sound. These speakers must be connected to the output jack (device that can receive a plug) of the computer’s sound card.

III. Assignments:

ü Name the output devices you know;

ü Tell about the output devices you usually use;

ü Describe the functions of your favorite output device;

ü Try to explain the difference between the input and output devices;

ü Try to name the devices that can function both as input and output ones.