Learn about the technologies behind the Internet with The TCP/IP Guide!
NOTE: Using robot software to mass-download the site degrades the server and is prohibited. See here for more.
Find The PC Guide helpful? Please consider a donation to The PC Guide Tip Jar. Visa/MC/Paypal accepted.
View over 750 of my fine art photos any time for free at DesktopScenes.com!

[ The PC Guide | Systems and Components Reference Guide | Video Cards | Video Display Standards ]

Video Graphics Adapter (VGA)

The replacement for EGA was IBM's last widely-accepted standard: the Video Graphics Array or VGA. VGA, supersets of VGA, and extensions of VGA form today the basis of virtually every video card used in PCs. Introduced in the IBM PS/2 model line, VGA was eventually cloned and copied by many other manufacturers. When IBM fell from dominance in the market, VGA continued on and was eventually extended and adapted in many different ways.

Most video cards today support resolutions and color modes far beyond what VGA really is, but they also support the original VGA modes, for compatibility. Most call themselves "VGA compatible" for this reason. Many people don't realize just how limited true VGA really is; VGA is actually pretty much obsolete itself by today's standards, and 99% of people using any variant of Windows are using resolution that exceeds the VGA standards. True VGA supports 16 colors at 640x480 resolution, or 256 colors at 320x200 resolution (and not 256 colors at 640x480, even though many people think it does). VGA colors are chosen from a palette of 262,144 colors (not 16.7 million) because VGA uses 6 bits to specify each color, instead of the 8 that is the standard today.

VGA (and VGA compatibility) is significant in one other way as well: they use output signals that are totally different than those used by older standards. Older displays sent digital signals to the monitor, while VGA (and later) send analog signals. This change was necessary to allow for more color precision. Older monitors that work with EGA and earlier cards use so-called "TTL" (transistor-transistor logic) signaling and will not work with VGA. Some monitors that were produced in the late 80s actually have a toggle switch to allow the selection of either digital or analog inputs. See here for more on the issue of analog and digital signalling.

Note that standard VGA does not include any hardware acceleration features: all the work of creating the displayed image is done by the system processor. All acceleration features are extensions beyond standard VGA.

Next: Super VGA (SVGA) and Other Standards Beyond VGA


Home  -  Search  -  Topics  -  Up

The PC Guide (http://www.PCGuide.com)
Site Version: 2.2.0 - Version Date: April 17, 2001
Copyright 1997-2004 Charles M. Kozierok. All Rights Reserved.

Not responsible for any loss resulting from the use of this site.
Please read the Site Guide before using this material.
Custom Search