Multicolor Graphics Adapter
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Multicolor Graphics Adapter (MCGA) was the IBM name for what would later become part of the generic Video Graphics Array (VGA) standard. The IBM PS/2 Model 25, introduced in 1987, shipped with MCGA built into the mainboard.
MCGA was similar to VGA in that it had a 256-color mode, but that was the extent of the chipset's abilities. VGA included a number of high-resolution display modes, but the 256-color mode proved most popular for gaming. The 256-color mode in VGA was sometimes referred to as MCGA even though MCGA only existed on the PS/2. No MCGA cards were ever made.
Display modes supported by MCGA were all CGA modes plus 640x480 monochrome, 60 Hz refresh rate, and 320x200, 256 colors (out of a palette of 262,144) at 70 Hz refresh rate. The display adapter used a 15-pin D-shell connector. Monochrome text modes compatible with the 5151 monitor were not supported.
One might consider MCGA to be a stepping stone between CGA and VGA. Interestingly, MCGA lacked EGA compatibility. (VGA, on the other hand, was fully backwards compatible.) This resulted in the frustrating situation where many EGA games (300x200 16 colors) would fall back to 4 color CGA mode (or not run at all), even though MCGA was capable of displaying 320x200 with 256 colors. Fortunately, many other 16 color EGA games (such as older adventure games from Sierra On-line and Lucasfilm Games) specifically supported MCGA in its 320x200 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.
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.
Reference
Scott Mueller Upgrading and Repairing PCs, Second Edition, Que Books, 1992, ISBN 0-88022-856-3