An output device is any peripheral device that converts machine-readable information into people-readable form such as a monitor, printer, plotter and voice output device.

Computer Display (Monitors)

A computer display is also called a display screen or video display terminal (VDT). A monitor is a screen used to display the output of a computer. Images are represented on monitors by individual dots called pixels. A pixel is the smallest unit on the screen that can be turned on and off or made different shades. The density of the dots determines the clarity of the images, the resolution.

• Screen resolution: This is the degree of sharpness of a displayed character or image. The screen resolution is usually expressed as the number of columns by the number rows. A 1024x768 resolution means that it has 1024 dots in a line and 768 lines. A smaller screen looks sharper on the same resolution. Other measures of display resolution are dot pitch and refresh rate.

• Interlaced/Non-interlaced: An interlaced technique refreshes the lines of the screen by exposing all odd lines first then all even lines next. A non-interlaced technology that is developed later refreshes all the lines on the screen form top to bottom. The non- interlaced method gives more stable video display than interlaced method. It also requires twice as much signal information as interlaced technology.

Cathode Ray Tubes (CRT)

A CRT is a vacuum tube used as a display screen for a computer output device. Although the CRT means only a tube, it usually refers to all monitors. IBM and IBM compatible microcomputers operate two modes unlike Macintosh based entirely on graphics mode. They are a text mode and a graphics mode. Application programs switch computers into appropriate display mode.

Monochrome Monitors

A monochrome monitor has two colors, one for foreground and the other for background. The colors can be white, amber or green on a dark (black) background. The monochrome monitors display both text and graphics modes.

Color Monitors

A color monitor is a display peripheral that displays more than two colors. Color monitors have been developed through the following paths.

• CGA: This stands for Color Graphics Adapter. It is a circuit board introduced by IBM and the first graphics standard for the IBM PC. With a CGA monitor, it is harder to read than with a monochrome monitor, because the CGA (320 X 200) has much fewer pixels than the monochrome monitor (640 X 350). It supports 4 colors.

• EGA: It stands for Enhanced Graphics Adapter. EGA is a video display standard that has a resolution of 640 by 350 pixels and supports 16 colors. EGA supports previous display modes and requires a new monitor.

• VGA: VGA stands for Video Graphics Array. This is a video display standard that provides medium to high resolution. In a text mode, the resolution of this board is 720 by 400 pixels. It supports 16 colors with a higher resolution of 640 by 480 pixels and 256 colors with 320 X 200 pixels.

• Super VGA: This is a very high resolution standard that displays up to 65,536 colors. Super VGA can support a 16.8 million colors at 800 by 600 pixels and 256 colors at 1024 by 768 pixels. A high-priced super VGA allows 1280 by 1024 pixels. Larger monitors (17" or 21" and larger) with a high resolution of 1600 by 1280 pixels are available. VESA (Video Electronics Standards Association) has set a standard for super VGA.

Flat Panel Displays

Portable computers such as a lap top use flat panel displays, because they are more compact and consume less power than CRTs. Portable computers use several kinds of flat panel screens:

Liquid-Crystal Displays (LCDs)

A display technology that creates characters by means of reflected light and is commonly used in digital watches and laptop computers. LCDs replaced LEDs (light emitting diodes) because LCDs use less power. LCDs are difficult to read in a strong light, because they do not emit their own light. Portable computers wanted to have brighter and easier to read displays. Backlit LCDs are used for the purpose now.

• Backlit LCDs: This is a type of LCD display having its own light source provided from the back of the screen. The backlit makes the background brighter and clear, as a result the texts and images appear sharper. However, this still is much less clear than CRTs. Thus, better technology is needed.

• Active Matrix LCDs: This is an LCD display technique in which every dot on the screen has a transistor to control it more accurately. This uses a transistor for each monochrome or each red, green and blue dot. It provides better contrast, speeds up screen refresh and reduces motion smearing.

Electroluminescent (EL) Displays

A flat panel display technology that actively emits light at each pixel when it is electronic charged. This provides a sharp, clear image and wide viewing angle. The EL display type of flat panel is better than LCD.

Gas Plasma Displays

This is also called a gas panel or a plasma panel and is another flat screen technology. A plasma panel contains a grid of electrodes in a flat, gas filled panel. The image can persist for a long time without refreshing in this panel. The disadvantages of the gas plasma displays are that they must use AC power and cannot show sharp contrast.

Refresh Rates: This is the number of times to repaint the screen each second. Generally, the higher the rate, the easier the monitor is on your eyes. However, 75 Hz is a point of diminishing returns.

Dot Pitch: This is another measure of resolution for a display screen. This is the width of an individual dot. For example, the width of a .26 dot pitch is 26/100ths millimeters. The smaller the dot pitch, the higher the resolution.