Multi-Color Graphics Array
The Multi-Color Graphics Array was a video subsystem built into the motherboard of the IBM PS/2 Model 30, introduced on April 2, 1987, and Model 25, introduced later on August 11; no standalone MCGA cards were ever made. The MCGA supported all CGA display modes plus 640×480 monochrome, 60 Hz refresh rate, and 320×200, 256 colors (out of a palette of 262,144) at 70 Hz refresh rate. The display adapter used a 15-pin D-shell connector. The MDA monochrome text mode was not supported.
MCGA was similar to VGA in that it had a 256-color mode (the 256-color mode in VGA was sometimes referred to as MCGA even though MCGA only existed on a small number of PS/2 models) and used 15-pin analog connectors, but the chipset's abilities were limited to that. MCGA lacked EGA compatibility, while VGA, on the other hand, was almost fully backward compatible with EGA. VGA also included other high-resolution display modes.
The 256-color mode proved most popular for gaming, but at the time the MCGA was introduced, many games lacking support for 256-color graphics were forced to fall back to four-color CGA mode (or not run at all) instead of using EGA video modes (320×200 16 colors). However, many other 16-color EGA games (such as older adventure games from Sierra On-line and Lucasfilm Games) specifically supported MCGA in its 320×200 256-color mode, picking the colors most resembling the 16-color RGB palette, while leaving the other available colors in that mode unused. 256-color VGA games ran fine on MCGA as long as they stuck to the basic 320×200 256-color mode and didn't attempt to use VGA-specific features such as multiple screen pages.
The tenure of MCGA was brief; the PS/2 Model 25 and Model 30 (which had an MCGA display adapter integrated into the motherboard) were discontinued by 1992 and no manufacturer produced a clone of this display adapter, since the VGA standard introduced at the same time was considered superior. MCGA was also rendered redundant to VGA since almost all the capabilities of MCGA were also part of VGA.
The help on screen modes for QuickBASIC 4.5 has some references to the MCGA adapter.
Scott Mueller Upgrading and Repairing PCs, Second Edition, Que Books, 1992, ISBN 0-88022-856-3