Video Graphics Array

Video Graphics Array (VGA) is the display hardware first introduced with the IBM PS/2 line of computers in 1987. Through widespread adoption, the term has also come to mean either an analog computer display standard, the 15-pin D-sub miniature VGA connector, or the 640×480 resolution characteristic of the VGA hardware.

VGA was the last IBM graphics standard to which the majority of PC clone manufacturers conformed, making it the lowest common denominator that virtually all post-1990 PC graphics hardware can be expected to implement. It was officially followed by IBM's Extended Graphics Array (XGA) standard, but was effectively superseded by numerous slightly different extensions to VGA made by clone manufacturers, collectively known as Super VGA.

Today, the VGA analog interface is used for high definition video, including resolutions of 1080p and higher. While the transmission bandwidth of VGA is high enough to support even higher resolution playback, there can be picture quality degradation depending on cable quality and length. How discernible this degradation is depends on the individual's eyesight and the display, though it is more noticeable when switching to and from digital inputs like HDMI or DVI.

The VGA supports both All Points Addressable graphics modes, and alphanumeric text modes.

Standard graphics modes

Standard graphics modes are:

·         640×480 in 16 colors or monochrome (the latter matching IBM's lesser Multi-Color Graphics Array standard)

·         640×350 or 640×200 in 16 colors or monochrome (EGA compatibility mode)

·         320×200 in 4 or 16 colors

·         320×200 in 256 colors (Mode 13h)

The 640×480 16-color and 320×200 256-color modes had fully redefinable palettes, with each entry selectable from within an 18-bit (262,144-color) RGB table, although the high resolution mode is most commonly familiar from its use with a fixed palette under Microsoft Windows. The other color modes defaulted to standard EGA or CGA compatible palettes (including the ability for programs to redefine the 16-color EGA palette from a master 64-color table), but could still be redefined if desired using VGA-specific programming.

Higher-resolution and other display modes

Higher-resolution and other display modes are also achievable, even with standard cards and most standard monitors – on the whole, a typical VGA system can produce displays with any combination of:

·         512 to 800 pixels wide, in 16 colors (including 640, 704, 720, 736, 768...), or

·         256 to 400 pixels wide, in 256 colors (including 320, 360, 384...) with

·         200, or 350 to 410 lines (including 400-line) at 70 Hz refresh rate, or

·         224 to 256, or 448 to 512 lines (including 240 or 480-line) at 60 Hz refresh rate

·         512 to 600 lines at reduced vertical refresh rates (down to 50 Hz, and including e.g. 528, 544, 552, 560, 576-line), depending on individual monitor compatibility.

(175 to 205 line modes may be possible at 70 Hz, and 256 to 300 lines in the 50 to 60 Hz refresh rate range, as well as horizontal widths below 256/512, but these are of little practical use)

For example, high resolution modes with square pixels are available at 768×576 or 704×528 in 16 colors, or medium-low resolution at 320×240 with 256 colors; alternatively, extended resolution is available with "fat" pixels and 256 colors using, e.g. 400×600 (50 Hz) or 360×480 (60 Hz), and "thin" pixels, 16 colors and the 70 Hz refresh rate with e.g. 736×410 mode.

"Narrow" modes such as 256×224 tend to preserve the same pixel ratio as in e.g. 320×240 mode unless the monitor is adjusted to stretch the image out to fill the screen, as they are derived simply by masking down the wider mode instead of altering pixel or line timings, but can be useful for reducing memory requirements and pixel addressing calculations for arcade game conversions or console emulators.

Standard text modes

Standard text modes:

·         80×25 character display, rendered with a 9×16 pixel font, with an effective resolution of 720×400 in either 16 colors or monochrome, the latter being compatible with legacy MDA-based applications.

·         40×25, using the same font grid, for an effective resolution of 360×400

·         80×43 or 80×50 (8×8 font grid) in 16-colors, with an effective resolution of 640×344 (EGA-compatible) or 640×400 pixels.

As with the pixel-based graphics modes, additional text modes are technically possible (as VGA resolution settings are notionally calculated from character-grid dimensions) with an overall maximum of about 100×80 cells and an active area spanning about 88×64 cells, but these are rarely used as it usually makes much more sense to just use a graphics mode – with a small, perhaps proportional font – if a larger text display is required. One variant that is sometimes seen is 80×30 or 80×60, using an 8×16 or 8×8 font and an effective 640×480 pixel display, which trades use of the more flicker 60 Hz mode for an additional 5 or 10 lines of text and square character blocks (or, at 80×30, square half-blocks).

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