Hardware Reference
In-Depth Information
The mating VGA cable connector that plugs into this connector normally has pin 9 miss-
ing. This was designed such that the mating hole in the connector on the video card could
be plugged, but it is usually open (and merely unused) instead. The connector is keyed by
virtue of the D-shape shell and pin alignment, so it is difficult to plug in backward even
without thekeypin.Pin5isusedonlyfortesting purposes,andpin15israrelyused;they
are often missing as well. To identify the type of monitor connected to the system, some
early VGA cards used the presence or absence of the monitor ID pins in various combin-
ations.
In addition to the connector and electrical interface, the original VGA standard also
defined a number of text and graphics display modes with various resolutions and colors.
The original VGA modes allowed for a maximum graphics resolution of 640×480 in only
16 (4-bit) colors. This was the maximum that could be supported by the original 256KB
of RAM included on the card.
IBM introduced higher-resolution versions of VGA called XGA and XGA-2 in the early
1990s, but most of the development of VGA standards has come from the third-party
video card industry and its trade group, the Video Electronic Standards Association
(VESA;
www.vesa.org
). When VGA originated in 1987, it had low resolution and color
capabilitybytoday'sstandards.Sincethen,VGAhasevolvedtosupporthigherresolution
modes with many more colors. Even the least-expensive video adapters on the market
today can work with modes well beyond the original VGA standard.
