Various computer display standards or display modes have been used in the history of the
personal computer. They are often a combination of
display resolution (specified as the width and height in
pixels), color depth (measured in
bits), and
refresh rate (expressed in
hertz). Associated with the screen resolution and refresh rate is a display adapter. Earlier display adapters were simple frame-buffers, but later display standards also specified a more extensive set of display functions and software controlled interface.
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IBM and others have introduced a bewildering plethora of graphics and text display
standards for
IBM PCs. The standards are mostly implemented by plugging in a video display board (or "
graphics adaptor") and connecting the appropriate monitor to it. Each new standard subsumes its predecessors. For example, an
EGA board can also do
CGA and
MDA.
With the
PS/2, IBM introduced the
VGA standard and built it into the main system board
motherboard. VGA is also available as a plug-in board for PCs from third-party vendors. Also with the PS/2, IBM introduced the
8514 high-resolution graphics standard. An 8514 adaptor board plugs into the PS/2, providing a dual-monitor capability.
Graphics software has to support the major IBM graphics standards and many non-IBM, proprietary standards for high-resolution displays. Either software vendors provide
display drivers, or display vendors provide drivers for the software package. In either case, switching software or switching display systems is fraught with compatibility problems.
Display Resolution Colours Sponsor Systems
MDA 720x350 T 2 IBM PC CGA 320x200 4 IBM PC EGA 640x350 16 IBM PC PGA 640x480 256 IBM PC
Hercules 729x348 2 non-IBM PC
MCGA 720x400 T 320x200 G 256 PS/2
VGA 720x400 T 640x480 G 16
SVGA 800x600 16 VESA
XVGA 1024x768 256 (IBM name: 8514)
T: text, G: graphics.
More colours are available from third-party vendors for some display types.
See also
MDA,
CGA,
EGA,
PGA,
Hercules,
MCGA,
VGA,
SVGA,
8514,
VESA.
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