Enhanced Graphics Adapter
Enhanced Graphics Adapter is a graphic display specification between CGA and VGA. Introduced in 1984, EGA produced a display of 16 colors at a resolution of 640x350 pixels. Each of the 16 colours could be assigned a unique RGB colour via a palette mechanism in this high-resolution mode; EGA let you choose the colours out of a total of 64 (2 bits per pixel for red, green and blue). EGA also included full 16-colour versions of the CGA 640x200 and 320x200 graphics modes; only the 16 CGA/RGBI colours are available in these modes. The original CGA modes are also present, though the EGA isn't 100% hardware compatible with the CGA. EGA can also drive a MDA monitor by setting the switches on the board a certain way; 640x350 is the only resolution available in this case.
The base IBM EGA card came with 64 kilobytes of video memory installed, just enough to handle monochrome high-resolution graphics (but allowed full colour in 640x200 and 320x200 modes). Later on, most EGA cards and clones came with a full 256 kilobytes of memory. A few third-party EGA clones (notably ATI and Paradise boards) featured extended graphics modes (640x400, 640x480 and 720x540 were common), automatic monitor type detection, and 400-line mode on CGA monitors (accomplished using interlacing).