Editing Video Graphics Array (section)

=== Programming ===
{{Unreferenced section|date=September 2024}}
"Unchaining" the 256&nbsp;KB VGA memory into four separate "planes" makes VGA's 256&nbsp;KB of RAM available in 256-color modes. There is a trade-off for extra complexity and performance loss in some types of graphics operations, but this is mitigated by other operations becoming faster in certain situations:

*Single-color polygon filling could be accelerated due to the ability to set four pixels with a single write to the hardware.
*The video adapter could assist in copying video RAM regions, which was sometimes faster than doing this with the relatively slow CPU-to-VGA interface.
*The use of multiple video pages in hardware allowed [[double buffering]], [[triple buffering]] or split screens, which, while available in VGA's {{resx|320x200}} 16-color mode, was not possible using stock [[Mode 13h]].
*Most particularly, several higher, arbitrary-resolution display modes were possible, all the way up to the programmable limit of {{resx|800x600}} with 16&nbsp;colors (or {{resx|400x600}} with 256 colors), as well as other custom modes using unusual combinations of horizontal and vertical pixel counts in either color mode.

Software such as [[Fractint]], [[Xlib]] and ColoRIX also supported tweaked 256-color modes on standard adaptors using freely-combinable widths of 256, 320, and 360&nbsp;pixels and heights of 200, 240 and 256 (or 400, 480 and 512)&nbsp;lines, extending still further to 384 or 400 pixel columns and 576 or 600 (or 288, 300). However, {{resx|320x240}} was the best known and most frequently used, as it offered a standard 40-column resolution and 4:3 aspect ratio with square pixels. "{{resx|320x240}}&nbsp;×&nbsp;8" resolution was commonly called [[Mode X]], the name used by [[Michael Abrash]] when he presented the resolution in [[Dr. Dobb's Journal]].

The highest resolution modes were only used in special, opt-in cases rather than as standard, especially where high line counts were involved. Standard VGA monitors had a fixed line scan (H-scan) rate{{snd}}"multisync" monitors being, at the time, expensive rarities{{snd}}and so the vertical/frame (V-scan) [[refresh rate]] had to be reduced in order to accommodate them, which increased visible [[Flicker (screen)|flicker]] and thus [[eye strain]]. For example, the highest {{resx|800x600}} mode, being otherwise based on the matching SVGA resolution (with 628 total lines), reduced the refresh rate from 60&nbsp;Hz to about 50&nbsp;Hz (and {{resx|832x624}}, the theoretical maximum resolution achievable with 256&nbsp;KB at 16 colors, would have reduced it to about 48&nbsp;Hz, barely higher than the rate at which XGA monitors employed a double-frequency interlacing technique to mitigate full-frame flicker).

These modes were also outright incompatible with some monitors, producing display problems such as picture detail disappearing into [[overscan]] (especially in the horizontal dimension), vertical roll, poor [[horizontal sync]] or even a complete lack of picture depending on the exact mode attempted. Due to these potential issues, most VGA tweaks used in commercial products were limited to more standards-compliant, "monitor-safe" combinations, such as {{resx|320x240}} (square pixels, three video pages, 60&nbsp;Hz), {{resx|320x400}} (double resolution, two video pages, 70&nbsp;Hz), and {{resx|360x480}} (highest resolution compatible with both standard VGA monitors and cards, one video page, 60&nbsp;Hz) in 256 colors, or double the horizontal resolution in 16-color mode.