Computer Output Devices : The information processed by the computer is translated into a form that we understand, and displayed by these machines. Normally, the output is classified as Softcopy Output or Sound Output and Hardcopy Output.

Softcopy refer to data that is shown on a display screen or is in audio or voice form. This kind of output is not tangible; it cannot be touched. Virtual reality and robots might also be considered softcopy devices. Hardcopy refer to printed output. The principal examples are printouts, whether text or graphics, from printers, plotters etc.

Display screens: also known as CRTs, monitors, or simply screens, differ in size, color, resolution, and video display adapter card. These are used for inputting the data or displaying the information after processing.

Size: monitor come in different sizes, from small screen built into palmtops and laptop to extra large monitors used for special purposes.

Color: Many monitors display color. These RGB displays can create 256 colors and several thousand variations on them by blending shades of Red, Green, and Blue (RGB). Monochrome displays show information using a single foreground color on a contrasting background color.

Resolution: All the characters and images on a monitor are made up of dot patterns; the number of dot, or pixels, per inch determines resolution, or the sharpness of the image. A higher number of pixels means a shaper image.

Video Display Adapters: to display graphics, a display screen must have a video display adapter attached with the computer. It is known as a video graphics card, and is a circuit board that determines the resolution, number of colors, and speed with images appear or the display screen. So far, there are three types of graphics cards introduced in the market.

VGA:  video graphics array, support 16-256 colors, depending on screen resolution. At 320 x 200 pixels, it will support 16 colors and at 640 x 480 pixels, 256 colors. It is called 4-bit color.


LCD screen


Flat Screen


Normal Screen

SVGA: super video graphics array, support 256 colors at higher resolution than VGA. It has two graphics modes: 800 x 600 pixels and 1024 x 768 pixels. It is called 8-bit color.

XGA: Extended graphics array, supports up to 16.7 million colors at a resolution of 1024 x 768 pixels. Depending on the video display adapter memory chip, XGA will support 256, 65536, ro 16, 777,216 colors. It is called 24-bit color or true color.

Types of screen: display screens are of two types i.e. Cathode-Ray Tubes and Flat-Panel Displays.

CRT (Cathode-Ray Tubes): the most common form of display screen is the computer or video display terminal. This same kind of technology is found not only in the screens of desktop computers but also in television set and in fight-information monitors in airport. A stream of bits defining the image is sent from the computer (from the CPU) to the CRT’s electron gun, where the bits are converted to electrons. The inside of the front of the CRT screen is coated with phosphor. When a beam of electrons from the electron gun (deflected through a yoke) hits the phosphor, it lights up selected pixels to generate an image on the screen.

crt-screen-worksHow CRT screen work

Flat-Panel Displays: The flat-panel displays are much thinner, weightless, and consume less power to CRT. Thus, they are better for portable computers. Flat-panel displays are made up of two plates of glass with a substance in between them, which is activated in different ways. There are three types of technology used in flat-panel display screens: LCD (Liquid-Crystal Display) consists of a substance called liquid crystal, the molecules of which line up in a way that lighting behind the screen is blocked or allowed through to create an image. EL (Electro-Luminescent Display) contain a substance that glows when it is charged by an electric current. Gas-plasma display is like a neon bulb, in which the display uses a gas that emits light in the presence of an electric current.

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