MCGA

MultiColor Graphics Array, released in 1987, marked a switch-over in video standards that would eventually lead into VGA and SVGA which we now use today. It was integrated into the motherboards of old PS/2 models 25 and 30. When coupled with a proper IBM display, it supported all CGA modes, but it was not compatible with previous monitors due to the fact that MCGA used analog video signals rather than the TTL signals, which is what the older formats used. TTL stands for transistor-to-transistor logic, and is basically a form of logic which used voltage levels in the transistor to determine 0 or 1, on or off. TTL-based video signals did not allow for variability in the colors because on or off were the only two choices on any given signal. With analog signals, many more color variations were allowable, and the MCGA interface could generate up to 256 colors.

With the switch from TTL to analog, MCGA also heralded the change from the 9-pin connector to the full 15-pin connector which we are used to using today.

8514/A

8514/A is a standard produced by IBM in 1987 to work with its MCA bus. It worked well, producing high resolutions on interlaced monitors. A later adaption allowed fast refresh rates on noninterlaced monitors, producing high quality flicker free images. 8514/A works quite differently than a VGA, although they both use the same kind of monitor. On a 8514/A, the computer tells the video card what to do and the video card figures out how to do it. For example, it says “Draw a circle” and the card figures it out. These are higher level commands and are quite different than the pixel by pixel instructions which must be calculated by the CPU in standard VGA cards.

This standard was ahread of its time. 8514/A cards are much faster than VGA cards and often provide higher quality images than the VGA card. Nevertheless, lack of support dealt the standard an early death. IBM discontinued this format in favor of the more advanced XGA, which was released in 1990 and basically allowed more simultaneous colors.  XGA went on to become the standard for MicroChannel PC platforms.

VGA

VGA stands for Video Graphics Array. It was introduced on April 2, 1987 by IBM, the same day it introduced the MCGA and 8514/A adapters. Although all three were advances for the time, only VGA became increasingly popular. VGA, although now more advanced, has become the standard for desktop video, leaving both the MCGA and 8514 forgotten despite the fact that it is strikingly similar to MCGA.

IBM PS/2 systems contained the VGA circuitry on a single VLSI chip which was integrated onto the motherboard. In order for users to use the new adapter in earlier systems, IBM developed the PS/2 Display Adapter, or the VGA video card. This card contained all the circuitry needed to produce VGA graphics, and like all expansion cards, it plugged into a slot on the motherboard, via an 8-bit interface. In the light of advances, IBM has discontinued this basic VGA card, although many third party cards were available for the PC. Today, the VGA card is not much used, and usually serves as a “spare”.

VGA offered clean images at higher resolutions. The standard VGA could produce as many as 256 colors at a time from a palette of 262,144 colors. The original VGA, though, had to be at a 320×400 resolution to display this amount of color. At the standard 640×480 resolution, it was only capable of 16 colors at a time. Also, VGA extends into the monochrome world. IT uses color summing to translate color graphics into graphics using 64 different shades of grey. This, in effect, simulates color on a monochrome monitor. VGA requires a VGA monitor, or one capable of accepting the analog output of a VGA card.