VGA Graphics Card - Video Graphics Array (VGA)

VGA (Video Graphics Array) is an older analog video technology, and represents the minimum compatibility standard for the use of Cathode Ray Tube (CRT) monitors with modern computer operating systems. VGA-style graphics are visible during the boot-up process on Windows-based systems when the BIOS and start-up diagnostic screens are displayed.

VGA Graphics Card Palette and Resolution

Standard VGA graphics mode is generally limited to a 640 x 480 resolution, much smaller than the standard desktop sizes allowed used by modern graphics cards

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VGA uses either a 16 or 256 at a time, chosen from an overall maximum color palette of 262,144 colors. This format of color selection is widely known as 8-bit color.

VGA and 8-Bit Color

In most video systems that use 8-bit color, an image file - or palette - is stored in the video memory or RAM of the host computer along with the raw image data. The advantage over older methods of producing images is that the global palette in the video memory can be overwritten by the palette of any particular image, allowing a much greater range of overall colors available on-screen at any given time.

The local image palette holds up to 256 colors, and assigns a value to each pixel drawn that matches one of these colors. The color-matching information must be expressed in a single 8-bit byte, thus this format is most often referred to "8-bit color."

8-bit color is almost never used on applications that presently exist, since the inherent palette limitations tend to produce images that are dithered, or appear highly pixelated and fuzzy.

Some exceptions are Virtual Network Computing and Remote Desktop Protocol, which sometimes switch to an 8-bit color structure to conserve bandwidth while operating remotely.

Video Graphics Array (VGA) History

IBM introduced the Enhanced Graphics Adapter (EGA) in 1984 to replace the aging Color Graphics Adapter (CGA) for CRT display devices. The release of EGA was timed to correspond with the release of IBM's Advanced Technology line. EGA boasted a resolution of 350x640 with a maximum 16 color palette, nearly doubling the output of the old CGA technology.

In 1987, IBM released yet another upgrade - VGA - to replace existing EGA technology for CRT display devices. Offering (at the time) an even larger color palette and greater resolution, VGA quickly became the widespread standard in video processing for computer display devices.

Even graphics cards produced today still include instructions for displaying objects in standard VGA format, although this resolution is generally only visible is there is an error with the higher functions of the graphics card, if the computer is operating in Safe Mode, or if the video drivers have been improperly installed.

IBM replaced VGA in 1990 with XGA (eXtended Graphics Array), but it met with little success. The Video Electronics Standards Association (VESA) was founded in 1989 to "Set and support industry-wide interface standards designed for the PC, workstation, and other computing environments."

VESA released specifications for a technology dubbed Super Video Graphics Array (SVGA) the same year that IBM released XGA. SVGA went on to become the industry standard for the next decade, and XGA was largely forgotten.

SVGA - Super VGA

Super VGA standards exceeded standard VGA in all respects. SVGA offered a maximum resolution of 1024 x 768, and was built around a color palette of 65,536 colors as opposed to the 256 color palette of VGA

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This new, massive color palette was achieved by using 16-bit color(1B) rather than the old 8-bit format, which allowed two bytes of information per color rather than only one. This exponentially increased the maximum number of colors.

Or, to put it another way, by allowing two bytes of information instead of one, the existing maximum of 256 color definitions on a single 8-bit string of information is multiplied by the maximum 256 colors on the second string: 256 x 256 = 65,536.

Further, the overall palette of SVGA supported a whopping 16 million colors as opposed to the maximum color palette of 262,144 available from the standard VGA format.

16-bit color was the direct precursor to True Color, the method of color-selection used by most graphics cards today.

The VGA Video Card Port

VGA ports on a graphics card are identifiable by their trademark 15-pin DE-15 connector, visible on the outside of the graphics card as a trapezoid-shaped plug with three rows of holes. This connector is often referred by many different names:

Or sometimes, by industry experts, as simply the "15." The VGA connection carries messages to the CRT which define the values of Red, Green, Blue, horizontal sync, and vertical sync in analog format. It should be noted that while the VGA card itself is an analog device, the calculations that take place inside the card are entirely digital.

VGA Cables

There have never been industry standards for VGA cables, but better cables typically protect the internal coaxial wiring with enough insulation to prevent signal interference.

Signal crosstalk happens when the currents traveling through one cable generate an electro- magnetic interference with another nearby cable. This is why proper insulation is important - to ensure that the signal remains undiluted as it travels from the display output to the display device.

Another common cabling error is ghosting, which is a form of internal signal reflection that happens in poorly constructed cabling.

Longer cables are more prone to the effects of both crosstalk and ghosting, therefore it is recommended that users implement the shortest possible cabling when using VGA technology.