The Enhanced Graphics Adapter (EGA) is the IBM PC computer display standard specification located between CGA and VGA in terms of graphics performance (that is, colour and space resolution). Introduced in 1984 by IBM for its new PC-AT, EGA produced a display of 16 colors at a resolution of up to 640×350 pixels.
Each of the 16 colours could be assigned a unique RGB colour code via a palette mechanism in the 640×350 high-resolution mode; EGA let you choose the displayed colours out of a total of 64 palette colours (two bits per pixel for red, green and blue). EGA also included full 16-colour versions of the CGA 640×200 and 320×200 graphics modes; only the 16 CGA/RGBI colours are available in these modes. The original CGA modes are also present, though EGA isn't 100% hardware compatible with CGA. EGA can drive an MDA monitor by a special setting of switches on the board; only 640×350 high-res is available in this mode.
The base IBM EGA card came with 64 kilobytes of video memory installed, actually just enough to handle monochrome high-resolution graphics (but allowing for full colour in the 640×200 and 320×200 modes). Eventually, most EGA cards and clones would come with a full 256 KB of memory. A few third-party EGA clones
(notably the ATI Technologies and Paradise boards) featured a range of extended graphics modes (e.g. 640×400, 640×480 and 720×540), as well as automatic monitor type detection, and sometimes also a special 400-line interlace mode for use on CGA monitors.
The EGA standard was made obsolete by the introduction of VGA by IBM in April 1987 with the PS/2 computer line.
Also introduced in 1984, and obsoleted by 1987, the Professional Graphics Adapter offered slightly higher resolution and color depth than the EGA, up to 640 x 480 and 256 colours at 60 frames/second. It was intended for the computer-aided design market CAD and included 320 K of display RAM and an on-board microprocessor, which gave it the ability to do 3-d rotation and clipping of images. This display adapter consumed three of the expansion slots on the XT or AT motherboard. While never widespread in consumer-class personal computers, at $4,290 list price it compared to $50,000 dedicated CAD workstations of the time.
