Video Graphics Array

Lore & Background

VGA was the last IBM graphics standard to which the majority of IBM PC compatible computer manufacturers conformed, making it the lowest common denominator that virtually all post-1990 PC graphics hardware can be expected to implement. VGA was adapted into many extended forms by third parties, collectively known as Super VGA, then gave way to custom graphics processing units which, in addition to their proprietary interfaces and capabilities, continue to implement common VGA graphics modes and interfaces to the present day. The VGA analog interface standard has been extended to support resolutions of up to 2048×1536 for general usage, with specialized applications improving it further still.

Unlike the graphics adapters that preceded it (MDA, CGA, EGA and many third-party options), there was initially no discrete VGA card released by IBM. The first commercial implementation of VGA was a built-in component of the IBM PS/2, in which it was accompanied by 256 KiB of video RAM, and a new DE-15 connector replacing the DE-9 used by previous graphics adapters. IBM later released the standalone IBM PS/2 Display Adapter, which utilized the VGA but could be added to machines that did not have it built in. The color palette RAM and its corresponding DAC were integrated into one chip (the RAMDAC) and the CRTC was integrated into a main VGA chip, which eliminated several other chips in previous graphics adapters, so VGA only additionally required external video RAM and timing crystals.

Unlike the cards that preceded it, which used binary TTL signals to interface with a monitor, the VGA introduced a video interface using pure analog RGB signals, with a range of 0.7 volts peak-to-peak max. In conjunction with a 18-bit RAMDAC (6-bit per RGB channel), this produced a color gamut of 262,144 colors. The VGA supports all graphics modes supported by the MDA, CGA and EGA cards, as well as multiple new modes, including 640×480 in 16 colors or monochrome and 320×200 in 256 colors (Mode 13h).

Reader's Guide

VGA's significance lies in its role as the last IBM graphics standard to achieve near-universal conformity among IBM PC compatible manufacturers, establishing it as the lowest common denominator for PC graphics hardware after 1990. Its 640×480, 16-color mode became the de facto lowest common denominator of graphics cards, and by the mid 1990s, operating systems such as Windows 95 and OS/2 Warp 3.0 expected this mode, providing no support for lower resolutions or bit depths without additional drivers. Well into the 2000s, even after the VESA standard for graphics cards became commonplace, the VGA graphics mode remained a compatibility option for PC operating systems.

The VGA analog interface standard has been extended to support resolutions of up to 2048×1536 for general usage, with specialized applications improving it further still. VGA was adapted into many extended forms by third parties, collectively known as Super VGA, then gave way to custom graphics processing units which continue to implement common VGA graphics modes and interfaces to the present day. The term VGA now encompasses the computer display standard, the 15-pin D-subminiature connector, and the 640×480 resolution characteristic of the original hardware.

Did You Know?

• VGA was first introduced with the IBM PS/2 line of computers in 1987.
• The VGA connector uses 15 pins in a D-subminiature (DE-15) form, replacing the DE-9 used by previous adapters.
• VGA introduced a pure analog RGB video interface, unlike the binary TTL signals used by earlier cards.