Video technologies differ in many different
ways. However, the major 2 differences are resolution and the number of colors it
can produce at those resolutions.
Resolution
Resolution is the number of pixels that are used to draw an image on the screen. If you could count the pixels in one horizontal row across the top of the screen, and the number of pixels in one vertical column down the side, that would properly describe the resolution that the monitor is displaying. It’s given as two numbers. If there were 800 pixels across and 600 pixels down the side, then the resolution would be 800 X 600. Multiply 800 times 600 and you’ll get the number of pixels used to draw the image (480,000 pixels in this example). A monitor must be matched with the video card in the system. The monitor has to be capable of displaying the resolutions and colors that the adapter can produce. It works the other way around too. If your monitor is capable of displaying a resolution of 1,024 X 768 but your adapter can only produce 640 X 480, then that’s all you’re going to get.
When we talk about the different
technologies, we’re talking about the video card and monitor that make up that
display system. Also, standards describe the basic number of colors and
resolutions for each technology, but individual manufacturers always take
liberties, providing options and enhancements that are designed to make their
product more appealing to the end user. This is, of course, how new standards
come about.
Monochrome
Monochrome
Monochrome monitors are very basic displays that produce only one color. The basic text mode in DOS is 80 characters across and 25 down. When graphics were first introduced, they were fairly rough by todays standards, and you had to manually type in a command to change from text mode to graphics mode. A company called 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 fly whenever the application required it. Today’s adapters still basically use the same methods.
CGA/EGA
The Color Graphics Adapter (CGA) introduced color to the personal computer. In APA mode it can produce a resolution of 320 X 200 and has a palette of 16 colors but can only display 4 at a time. With the introduction of the IBM Enhanced Graphics Adapter (EGA), the proper monitor was capable of a resolution of 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 be either 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 the intensity 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 could produce 64 different levels of intensity. Their new Video Graphics Array adapter was capable of a resolution of 640 X 480 pixels and could display up to 256 colors from a palette of over 260,000. This technology soon became the standard for almost every video card and monitor being developed.
SVGA
Once again, manufacturers began to develop video adapters that added features and enhancements to the VGA standard. Super-VGA is based on VGA standards and describes display systems with several different resolutions and a varied number of colors. When SVGA first came out it could be defined as having capabilities of 800 X 600 with 256 colors or 1024 X 768 with 16 colors. However, these cards and monitors are now capable of resolutions 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 Channel Architecture expansion slots. It had its own coprocessor and bus-mastering ability, which means that it had the ability to execute instructions independent of the CPU. It was also a 32-bit adapter capable of increased data transfer speeds. XGA allowed for better performance, could provide higher resolution and more colors than the VGA and SVGA cards at the time. However, it was only available for IBM machines. Many of these features were later incorporated by other video card manufacturers.