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superseded by numerous slightly different extensions to VGA made by clone manufacturers, collectively known as Super VGA.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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