Video technologies differ in many differentways. However, the major 2 differences are resolution and the number of colors itcan produce at those resolutions.
Resolution
Resolution is the number of pixels that are used to draw an image on thescreen. If you could count the pixels in one horizontal row across the top ofthe screen, and the number of pixels in one vertical column down the side, thatwould properly describe the resolution that the monitor is displaying. It’sgiven as two numbers. If there were 800 pixels across and 600 pixels down theside, then the resolution would be 800 X 600. Multiply 800 times 600 and you’llget the number of pixels used to draw the image (480,000 pixels in thisexample). A monitor must be matched with the video card in the system. Themonitor has to be capable of displaying the resolutions and colors that theadapter can produce. It works the other way around too. If your monitor iscapable of displaying a resolution of 1,024 X 768 but your adapter can onlyproduce 640 X 480, then that’s all you’re going to get.
When we talk about the differenttechnologies, we’re talking about the video card and monitor that make up thatdisplay system. Also, standards describe the basic number of colors andresolutions for each technology, but individual manufacturers always takeliberties, providing options and enhancements that are designed to make theirproduct more appealing to the end user. This is, of course, how new standardscome about.
Monochrome
Monochrome
Monochrome monitors are very basic displays that produce only one color. Thebasic text mode in DOS is 80 characters across and 25 down. When graphics werefirst introduced, they were fairly rough by todays standards, and you had tomanually type in a command to change from text mode to graphics mode. A companycalled Hercules Graphics developed a video adapter that could do this for you.Not only could it change from text to graphics, but it could do it on the flywhenever the application required it. Today’s adapters still basically use thesame methods.
CGA/EGA
The Color Graphics Adapter (CGA) introduced color to the personal computer. InAPA mode it can produce a resolution of 320 X 200 and has a palette of 16colors but can only display 4 at a time. With the introduction of the IBMEnhanced Graphics Adapter (EGA), the proper monitor was capable of a resolutionof 640 X 350 pixels and could display 16 colors from a palette of 64.
VGA
Up until VGA, colors were produced digitally. Each electron beam could beeither on or off. There were three electron guns, one for each color, red,green and blue (RGB). This combination could produce 8 colors. By cutting theintensity of the beam in half, you could get 8 more colors for a total of 16.IBM came up with the idea of developing an analog display system that couldproduce 64 different levels of intensity. Their new Video Graphics Arrayadapter was capable of a resolution of 640 X 480 pixels and could display up to256 colors from a palette of over 260,000. This technology soon became thestandard for almost every video card and monitor being developed.
SVGA
Once again, manufacturers began to develop video adapters that added featuresand enhancements to the VGA standard. Super-VGA is based on VGA standards anddescribes display systems with several different resolutions and a variednumber of colors. When SVGA first came out itcould be defined as having capabilities of 800 X 600 with 256 colors or 1024 X768 with 16 colors. However, these cards and monitors are now capable ofresolutions up to 1280 X 1024 with a palette of more than 16 million colors.
XGA
Extended Graphics Array was developed by IBM. It improved upon the VGA standard(also developed by IBM) but was a proprietary adapter for use in Micro ChannelArchitecture expansion slots. It had its own coprocessor and bus-masteringability, which means that it had the ability to execute instructionsindependent of the CPU. It was also a 32-bit adapter capable of increased datatransfer speeds. XGA allowed for better performance, could provide higherresolution and more colors than the VGA and SVGA cards at the time. However, itwas only available for IBM machines. Many of these features were laterincorporated by other video card manufacturers.