View source for Video Graphics Array

{{Short description|Computer display standard and resolution}}
{{distinguish|Variable gauge}}
{{redirect|VGA|other uses|VGA (disambiguation)}}
{{Multiple issues|{{original research|date=November 2016}}
{{more citations needed|date=April 2019}}}}
{{Infobox graphics processing unit
| name = Video Graphics Array
| image = IBM VGA graphics card.jpg
| codename = 
| created = {{Start date and age|1987|04}}
| architecture = 
| transistors = 
| entry = {{ublist |{{nowrap|[[Chips and Technologies]] 82c441}} |[[Video Seven|Video-7]] VEGA Deluxe|[[ATI Technologies|ATI]] Graphics Solution Plus |{{longitem|{{hlist |[[S3 Graphics|S3]] (911|911A|924|801|805|805i|928|805p|928p)}}}} |[[Matrox]] MAGIC RGB |[[Plantronics]] Colorplus |[[Paradise Systems]] PEGA 1 |[[Tseng Labs]] ET3000 |[[Cirrus Logic]] CL-GD400s}}
| midrange = {{ublist|class=nowrap |[[ATI Wonder series]] |Paradise Systems PEGA 1a |[[S3 Graphics|S3]] Vision |[[Tseng Labs ET4000]] |[[Cirrus Logic]] CL-GD500s}}
| highend = {{ublist|class=nowrap |[[ATI Technologies|ATI]] [[ATI Mach|Mach series]] |Paradise Systems PEGA 2a |[[S3 Trio]] |Tseng Labs ET6000 |[[Cirrus Logic]] CL-GD5000s}}
| enthusiast = 
| openglversion = 
| d3dversion = 
| predecessor = {{ublist|class=nowrap ||[[Enhanced Graphics Adapter]] (EGA)|[[Professional Graphics Controller]] (PGC)}}
| successor = {{ublist|class=nowrap ||[[Super VGA|Super Video Graphics Array (SVGA)]]|[[Graphics display resolution#Extended Graphics Array|Extended Graphics Array (XGA)]]}}
}}

'''Video Graphics Array''' ('''VGA''') is a [[video display controller]] and accompanying de facto graphics standard, first introduced with the [[IBM PS/2]] line of computers in 1987,<ref name="pcmag">{{Cite magazine|last=Petzold|first=Charles|date=July 1987|title=Triple standard: three new video modes from IBM|url=https://books.google.com/books?id=LRBokcwLB70C&pg=PA131|magazine=PC Magazine|publisher=Ziff Davis|access-date=2020-04-13}}</ref><ref>{{cite web |title=Chronology of IBM Personal Computers |last=Polsson |first=Ken |url=http://pctimeline.info/ibmpc/ibm1987.htm |access-date=2015-01-28 |url-status=live |archive-url=https://web.archive.org/web/20150221071923/http://pctimeline.info/ibmpc/ibm1987.htm |archive-date=2015-02-21 }}</ref><ref>{{Cite news|url=https://www.computerhope.com/jargon/v/vga.htm|title=What is VGA (Video Graphics Array)?|access-date=2018-08-13|language=en}}</ref> which became ubiquitous in the [[IBM PC compatible]] industry within three years.<ref>{{Cite book|last=Enterprise|first=I. D. G.|url=https://books.google.com/books?id=coyDNO6C6OoC&q=computerworld%20VGA%20expected&pg=PA4|title=Computerworld|date=1990-10-22|publisher=IDG Enterprise|language=en}}</ref> The term can now refer to the [[computer display standard]], the 15-pin [[D-subminiature]] [[VGA connector]], or the {{resx|640x480}} [[Graphics display resolution|resolution]] characteristic of the VGA hardware.<ref>{{Cite web|title=Drawing In Protected Mode |website=OSDev Wiki|url=https://wiki.osdev.org/Drawing_In_Protected_Mode|access-date=2020-12-20}}</ref>

VGA was the last IBM graphics standard to which the majority of IBM PC compatible computer manufacturers conformed, making it the [[Lowest common denominator#Colloquial usage|lowest common denominator]] that virtually all post-1990 PC graphics hardware can be expected to implement.<ref name="computer.org">{{Cite web|url=https://www.computer.org/publications/tech-news/chasing-pixels/Famous-Graphics-Chips-IBMs-VGA|author=Dr. Jon Peddie|title=Famous Graphics Chips: IBM's VGA. The VGA was the most popular graphics chip ever|date=12 March 2019 |access-date=2020-04-13|quote=It is said about airplanes that the DC3 and 737 are the most popular planes ever built, and the 737, in particular, the best-selling airplane ever. The same could be said for the ubiquitous VGA, and its big brother the XGA. The VGA, which can still be found buried in today’s modern GPUs and CPUs, set the foundation for a video standard, and an application programming standard.}}</ref>

VGA was adapted into many extended forms by third parties, collectively known as [[Super VGA]],<ref>{{Cite news |last1=Eckert |last2=Azinger |date=April 15, 1991 |title=Product Comparison - Super VGA Boards |pages=53–63 |work=InfoWorld |url=https://books.google.com/books?id=4FAEAAAAMBAJ&q=super+VGA+infoworld&pg=PT50}}</ref> then gave way to custom [[graphics processing unit]]s which, in addition to their proprietary interfaces and capabilities, continue to implement common VGA graphics modes and interfaces to the present day.

The VGA analog interface standard has been extended to support resolutions of up to {{resx|2048x1536}} for general usage, with specialized applications improving it further still.{{Specify|date=April 2024}}<ref>{{Cite book|last=Magazines|first=S. P. H.|url=https://books.google.com/books?id=HOsDAAAAMBAJ&q=1080p%20vga&pg=PT65|title=HWM|date=April 2007|publisher=SPH Magazines|language=en}}</ref>

== Hardware design ==
[[File:IBM VGA 90X8941 on PS55.jpg|thumb|VGA section on the motherboard in [[IBM PS/55]] |alt=|left]]The [[Palette (computing)|color palette]] [[Random-access memory|random access memory]] (RAM) and its corresponding [[digital-to-analog converter]] (DAC) were integrated into one chip (the [[RAMDAC]]) and the [[cathode-ray tube]] controller ([[Video display controller#Types|CRTC]]) was integrated into a main VGA chip, which eliminated several other chips in previous graphics adapters, so VGA only additionally required external video RAM and [[timing crystal]]s.<ref>{{Cite web |last=Peddie |first=Jon |title=Famous Graphics Chips: IBM's VGA {{!}} IEEE Computer Society |url=https://www.computer.org/publications/tech-news/chasing-pixels/Famous-Graphics-Chips-IBMs-VGA/ |url-status=live |archive-url=https://web.archive.org/web/20221128083601/https://www.computer.org/publications/tech-news/chasing-pixels/Famous-Graphics-Chips-IBMs-VGA |archive-date=2022-11-28 |access-date=2022-12-27 |website=[[Institute of Electrical and Electronics Engineers#IEEE Computer Society|IEEE Computer Society]] |date=12 March 2019 |language=en-US}}</ref><ref>{{Cite journal |last=Thompson |first=Stephen |date=1988 |title=VGA ‒ Design choices for a new video subsystem |journal=IBM Systems Journal |publisher=IBM |volume=27 |issue=2 |pages=185‒197 |doi=10.1147/sj.272.0185}}</ref>

This small part count allowed IBM to include VGA directly on the PS/2 motherboard, in contrast to prior IBM PC models{{snd}}[[IBM Personal Computer|PC]], [[PC/XT]], and [[PC AT]]{{snd}}which required a separate display adapter installed in a slot in order to connect a monitor. The term "array" rather than "adapter" in the name denoted that it was not a complete independent expansion device, but a single component that could be integrated into a system.<ref name=":0" />

Unlike the graphics adapters that preceded it ([[IBM Monochrome Display Adapter|MDA]], [[Color Graphics Adapter|CGA]], [[Enhanced Graphics Adapter|EGA]] and many third-party options) there was initially no discrete VGA card released by IBM. The first commercial implementation of VGA was a built-in component of the IBM PS/2, in which it was accompanied by 256&nbsp;KB of video RAM, and a new DE-15 connector replacing the DE-9 used by previous graphics adapters. IBM later released the standalone ''IBM PS/2 Display Adapter'', which utilized the VGA but could be added to machines that did not have it built in.<ref>{{Cite web|date=1987-04-02|title=THE IBM PERSONAL SYSTEM/2 (TM) DISPLAY ADAPTER, THE IBM PERSONAL SYSTEM/2 DISPLAY ADAPTER 8514/A AND|url=https://www-01.ibm.com/common/ssi/printableversion.wss?docURL=/common/ssi/rep_ca/4/897/ENUS187-054/index.html&request_locale=en|access-date=2020-08-16|website=www-01.ibm.com|language=en-US}}</ref><ref name=":0">{{Cite news |last=Rosch |first=Winn |date=December 22, 1987 |title=IBM VGA Adapter Card: 256K Video RAM, 17 Display Modes |pages=35 |work=PC Magazine |url=https://books.google.com/books?id=gC-DsOtl2MgC&q=IBM+PS%2F2+display+adapter&pg=PA35}}</ref>

On some machines and cables, pin 9 was missing. All pin 9 does is power an EEPROM chip in the monitor which tells the graphics card the capabilities on the monitor. Systems or cables missing this are likely using an older version of VGA.

==Capabilities==
[[File:Birds VGA16.png|thumb|Simulated VGA {{resx|640x480}} 16 color image]]
[[File:Birds VGA256.png|thumb|Simulated VGA {{resx|320x200}} 256 color image (corrected for aspect ratio)]]
[[File:Vector Video Standards2.svg|thumb|Comparison of standard resolutions including VGA's 640&nbsp;×&nbsp;480|alt=]]
The VGA supports all graphics modes supported by the MDA, CGA and EGA cards, as well as multiple new modes.

===Standard graphics modes===
*{{resx|320x200}} in 4 or 16 colors (CGA/EGA compatibility)
*{{resx|320x200}} in 256 colors ([[Mode 13h]])
*{{resx|640x200}} and {{resx|640x350}} in 16 colors or monochrome (CGA/EGA compatibility)
*[[640×480|{{resx|640x480}}]] in 16 colors or [[monochrome]]<ref>{{cite web|last=Hinner|first=Martin|title=VGA Timings|url=http://martin.hinner.info/vga/timing.html|access-date=7 November 2012|url-status=live|archive-url=https://web.archive.org/web/20121027091012/http://martin.hinner.info/vga/timing.html|archive-date=27 October 2012}}</ref><ref>{{Cite web|title=Drawing In Protected Mode - OSDev Wiki|url=https://wiki.osdev.org/Drawing_In_Protected_Mode|access-date=2020-12-20|website=wiki.osdev.org}}</ref>

The {{resx|640x480}} 16-color and {{resx|320x200}} 256-color modes had fully redefinable palettes, with each entry selected from an [[List of monochrome and RGB color formats#18-bit RGB|18-bit (262,144-color)]] gamut.<ref name=":1">{{Cite patent|number=US5574478A|title=VGA color system for personal computers|gdate=1996-11-12|invent1=Bril|invent2=Pett|inventor1-first=Vlad|inventor2-first=Boyd G.|url=https://patents.google.com/patent/US5574478/en}}</ref><ref name=":2">{{Cite web |date=2017-12-26 |title=Reading and writing 18-bit RGB VGA Palette (pal) files with C# |url=https://www.cyotek.com/blog/reading-and-writing-18-bit-rgb-vga-palette-pal-files-with-csharp |access-date=2023-03-27 |website=The Cyotek Blog |language=en}}</ref><ref name=":3">{{Cite web |title=VGA/SVGA Video Programming--Color Registers |url=http://www.osdever.net/FreeVGA/vga/colorreg.htm |access-date=2023-03-27 |website=www.osdever.net}}</ref><ref name=":4">{{Cite web |title=VGA Palette Conversion \ VOGONS |url=https://www.vogons.org/viewtopic.php?t=38713 |access-date=2023-03-27 |website=www.vogons.org}}</ref>

The other modes defaulted to standard EGA or CGA compatible palettes and instructions, but still permitted remapping of the palette with VGA-specific commands.

==== {{resx|640x480}} graphics mode ====
The {{resx|640x480}} resolution (at 256 colors rather than 16) was originally used by IBM in [[Professional Graphics Controller|PGC]] graphics (which VGA offers no backward compatibility for) but did not see wide adoption until VGA was introduced. As the VGA began to be cloned in great quantities by manufacturers who added ever-increasing capabilities, its {{resx|640x480}}, 16-color mode became the de facto lowest common denominator of graphics cards. By the mid 1990s, a {{resx|640x480}}×16 graphics mode using the VGA memory and register specifications was expected by operating systems such as [[Windows 95]] and [[OS/2 Warp 3|OS/2 Warp 3.0]], which provided no support for lower resolutions or bit depths, or support for other memory or register layouts without additional drivers. Well into the 2000s, even after the [[VESA]] standard for graphics cards became commonplace, the "VGA" graphics mode remained a compatibility option for PC operating systems.

====Other graphics modes====
Nonstandard display modes can be implemented, with horizontal resolutions of:

*512 to 800 pixels wide, in 16 colors
*256 to 400 pixels wide, in 256 colors
And heights of:
*200, or 350 to 410 lines (including 400-line) at 70&nbsp;Hz refresh rate, or
*224 to 256, or 448 to 512 lines (including 240 or 480-line) at 60&nbsp;Hz refresh rate
*512 to 600 lines at reduced vertical refresh rates (down to 50&nbsp;Hz, and including e.g. 528, 544, 552, 560, 576-line), depending on individual monitor compatibility.
For example, high resolution modes with square pixels are available at {{resx|768x576}} or {{resx|704x528}} in 16 colors, or medium-low resolution at {{resx|320x240}} with 256 colors. Alternatively, extended resolution is available with "fat" pixels and 256 colors using, e.g. {{resx|400x600}} (50&nbsp;Hz) or {{resx|360x480}} (60&nbsp;Hz), and "thin" pixels, 16 colors and the 70&nbsp;Hz refresh rate with e.g. {{resx|736x410}} mode.

"Narrow" modes such as {{resx|256x224}} tend to preserve the same pixel ratio as in e.g. {{resx|320x240}} 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.

The PC version of [[Pinball Fantasies]] has the option to use non-standard modes "high res" modes, such as {{resx|640x350}}, allowing it to display a larger portion of the pinball table on screen.<ref>{{Cite web |title=Late PCI, early and middle AGP video chips DOS game compatibility test results |url=https://gona.mactar.hu/DOS_TESTS/#selection-125.18-125.26 |archive-url=https://archive.today/20220321183134/https://gona.mactar.hu/DOS_TESTS/#selection-125.18-125.26 |url-status=dead |archive-date=2022-03-21 |website=archive.ph}}</ref>

===Standard text modes===
{{See also|VGA text mode}}
VGA also implements several text modes:

*{{resx|80x25}}, rendered with a {{resx|9x16}} pixel font, with an effective resolution of {{resx|720x400}}<ref>{{cite web|last=Abrash|first=Michael|title=How 360×480 in 256 color mode works|url=http://www.phatcode.net/res/224/files/html/ch32/32-05.html|work=Graphics Programming Black Book|access-date=7 November 2012|url-status=live|archive-url=https://web.archive.org/web/20120423034027/http://www.phatcode.net/res/224/files/html/ch32/32-05.html|archive-date=23 April 2012}}</ref>
*{{resx|40x25}}, with a {{resx|9x16}} font, with an effective resolution of {{resx|360x400}}
*{{resx|80x43}} or {{resx|80x50}}, with an {{resx|8x8}} font grid, with an effective resolution of {{resx|640x344}} or {{resx|640x400}} pixels.

As with the pixel-based graphics modes, additional text modes are possible by programming the VGA correctly, with an overall maximum of about {{resx|100x80}} cells and an active area spanning about {{resx|88x64}} cells.

One variant that is sometimes seen is {{resx|80x30}} or {{resx|80x60}}, using an {{resx|8x16}} or {{resx|8x8}} font and an effective {{resx|640x480}} pixel display, which trades use of the more flickery 60&nbsp;Hz mode for an additional 5 or 10 lines of text and square character blocks (or, at {{resx|80x30}}, square half-blocks).

==Technical details==
Unlike the cards that preceded it, which used binary [[Transistor–transistor logic|TTL]] signals to interface with a monitor (and also [[Composite video|composite]], in the case of the CGA), the VGA introduced a video interface using pure analog [[Component video#RGB analog component video|RGB signals]], with a range of 0.7 volts peak-to-peak max. In conjunction with a [[Color depth#18-bit|18-bit]] [[RAMDAC]] (6-bit per RGB channel), this produced a color gamut of 262,144 colors.<ref name=":1" /><ref name=":2" /><ref name=":3" /><ref name=":4" />

The original VGA specifications follow:

*Selectable 25.175&nbsp;MHz<ref>{{Cite web|url=http://www.tinyvga.com/vga-timing/640x480@60Hz|title=VGA Signal 640 x 480 @ 60 Hz Industry standard timing|website=www.tinyvga.com}}</ref> or 28.322&nbsp;MHz master pixel clock
*Maximum of 640&nbsp;horizontal [[pixel]]s<ref name="ps2_refman1992">PS/2 Video Subsystem Technical Reference Manual 1992</ref> in graphics mode, and 720 pixels in text mode
*Maximum of 480&nbsp;lines<ref name="ps2_refman1992"/>
*[[Refresh rate]]s at 60 or 70&nbsp;[[Hertz|Hz]]<ref>{{cite web|title=VGA Signal timings|url=http://www.tinyvga.com/vga-timing|url-status=live|archive-url=https://web.archive.org/web/20160620145944/http://tinyvga.com/vga-timing|archive-date=2016-06-20}}</ref>
*[[Vertical blank interrupt]] <small>(Not all [[clone (computing)|clone]] cards support this.)</small>
*[[Planar (computer graphics)|Planar]] mode: up to 16&nbsp;colors <small>(4 [[bit plane]]s)</small>
*Packed-pixel mode: 256&nbsp;colors <small>([[Mode 13h]])</small>
*Hardware [[smooth scrolling]] support
*No [[Blitter]]
**Supports fast data transfers via "VGA latch" registers
*[[Barrel shifter]]
*[[Split screen (video games)|Split screen]] support

===Signal timings===
The intended standard value for the horizontal frequency of VGA's {{resx|640x480}} mode is exactly double the value used in the [[NTSC-M]] video system, as this made it much easier to offer optional [[TV-out]] solutions or external VGA-to-TV converter boxes at the time of VGA's development. It is also at least nominally twice that of CGA, which also supported [[composite monitor]]s.

All ''derived'' VGA timings (i.e. those which use the master 25.175 and 28.322&nbsp;MHz crystals and, to a lesser extent, the nominal 31.469&nbsp;kHz line rate) can be varied by software that bypasses the VGA firmware interface and communicates directly with the VGA hardware, as many MS-DOS based games did. However, only the standard modes, or modes that at least use almost exactly the same H-sync and V-sync timings as one of the standard modes, can be expected to work with the original late-1980s and early-1990s VGA monitors. The use of other timings may in fact damage such monitors and thus was usually avoided by software publishers.

Third-party "multisync" CRT monitors were more flexible, and in combination with "super EGA", VGA, and later SVGA graphics cards using extended modes, could display a much wider range of resolutions and refresh rates at arbitrary sync frequencies and pixel clock rates.

For the most common VGA mode ({{resx|640x480}}, 60&nbsp;Hz, [[progressive scan|non-interlaced]]), the horizontal timings can be found in the HP Super VGA Display Installation Guide and in other places.<ref name="Javier Valcarce timings list">{{cite web|title=Javier Valcarce VGA timings page|url=http://www.javiervalcarce.eu/wiki/VGA_Video_Signal_Format_and_Timing_Specifications|url-status=live|archive-url=https://web.archive.org/web/20150102175843/http://javiervalcarce.eu/wiki/VGA_Video_Signal_Format_and_Timing_Specifications|archive-date=2015-01-02}}</ref><ref>HP D1194A Super VGA Display & HP D1195A Ergonomic Super VGA Display Installation Guide, Hewlett Packard</ref>

===Typical uses of selected modes===
{{See also|Extended Display Identification Data}}
{{anchor|640×400}}
{{resx|640x400}} @ 70&nbsp;Hz is traditionally the video mode used for booting VGA-compatible [[x86]] [[personal computer]]s<ref name="epanorama_net-vga_timing">{{cite web|title=ePanorama.net - Circuits|url=http://www.epanorama.net/documents/pc/vga_timing.html|url-status=live|archive-url=https://web.archive.org/web/20090227050541/http://www.epanorama.net/documents/pc/vga_timing.html|archive-date=2009-02-27}} 090425 epanorama.net</ref> that show a graphical boot screen, while text-mode boot uses {{resx|720x400}} @ 70&nbsp;Hz.

This convention has been eroded in recent years, however, with POST and BIOS screens moving to higher resolutions, taking advantage of [[EDID]] data to match the resolution to a connected monitor.{{Citation needed|date=September 2024}}

{{resx|640x480}} @ 60&nbsp;Hz is the default Windows graphics mode (usually with 16&nbsp;colors),<ref name="epanorama_net-vga_timing" /> up to Windows 2000. It remains an option in XP {{citation needed span|date=September 2024|and later versions}} via the boot menu "low resolution video" option and per-application compatibility mode settings, despite newer versions of Windows now defaulting to {{resx|1024x768}} and generally not allowing any resolution below {{resx|800x600}} to be set.

The need for such a low-quality, universally compatible fallback has diminished since the turn of the millennium, {{clarify span|as VGA-signalling-standard screens or adaptors unable to show anything beyond the original resolutions have become increasingly rare.|date=September 2024}}

{{resx|320x200}} at 70&nbsp;Hz was the most common mode for early 1990s PC games, with pixel-doubling and line-doubling performed in hardware to present a {{resx|640x400}} at 70&nbsp;Hz signal to the monitor.

The [[Windows 9x|Windows 95/98/Me]] [[LOGO.SYS]] boot-up image was 320&nbsp;×&nbsp;400 resolution, displayed with pixel-doubling to present a {{resx|640x400}} at 70&nbsp;Hz signal to the monitor. The 400-line signal was the same as the standard {{resx|80x25}} text mode, which meant that pressing {{#invoke:key|press|Esc}} to return to text mode didn't change the frequency of the video signal, and thus the monitor did not have to resynchronize (which could otherwise have taken several seconds).{{Citation needed|date=September 2024}}

==Connector==
{{Main article|VGA connector}}
[[File:Vga-cable.jpg|thumb|A standard [[VGA connector]]]]
[[File:BNC connectors.jpg|thumb|VGA [[BNC connector|BNC connectors]]]]

The standard [[VGA connector|VGA monitor interface]] is a 15-pin [[D-subminiature|D-subminiature connector]] in the "E" shell, variously referred to as "DE-15", "HD-15" and erroneously "DB-15(HD)".

All VGA connectors carry [[Analog television|analog]] [[RGBHV]] (red, green, blue, [[horizontal sync]], [[vertical sync]]) video signals. Modern connectors also include [[Video Electronics Standards Association|VESA]] [[Display Data Channel|DDC]] pins, for identifying attached display devices.

Because VGA uses low-voltage analog signals, signal degradation becomes a factor with low-quality or overly long cables. Solutions include shielded cables, cables that include a separate internal [[coaxial cable]] for each color signal, and "broken out" cables utilizing a separate coaxial cable with a [[BNC connector]] for each color signal.

BNC breakout cables typically use five connectors, one each for Red, Green, Blue, Horizontal Sync, and Vertical Sync, and do not include the other signal lines of the VGA interface. With BNC, the coaxial wires are fully shielded end-to-end and through the interconnect so that virtually no crosstalk and very little external interference can occur. The use of BNC RGB video cables predates VGA in other markets and industries.

==Color palette==
{{See also|List of monochrome and RGB color formats|List of monochrome and RGB color formats#18-bit RGB|l2=18-bit RGB|List of 16-bit computer color palettes|List of 16-bit computer hardware palettes#MCGA and VGA|l4=MCGA and VGA}}
[[file:VGA palette with black borders.svg|thumb|VGA 256 default color palette]]
[[file:VGA palette organised.svg|thumb|VGA palette organised into 4 groups]]
[[file:Torak.gif|thumb|Examples of VGA images in 640×480 with 16 colors and 320×200 with 256 colors (bottom). [[Dither]]ing is used to mask color limitations.]]
The VGA color system uses register-based palettes to map colors in various bit depths to its 18-bit output gamut. It is [[backward compatible]] with the EGA and CGA adapters, but supports extra [[Bit depth (computer graphics)|bit depth]] for the palette when in these modes.

For instance, when in EGA 16-color modes, VGA offers 16 palette registers, and in 256-color modes, it offers 256 registers.<ref>{{Cite web|title=VGA/SVGA Video Programming--Color Regsters|url=http://www.scs.stanford.edu/17wi-cs140/pintos/specs/freevga/vga/colorreg.htm|access-date=2020-08-16|website=www.scs.stanford.edu}}</ref> Each palette register contain a [[List of monochrome and RGB color formats#18-bit RGB|3×6 bit]] RGB value, selecting a color from the 18-bit gamut of the [[Digital-to-analog converter|DAC]].

These color registers are initialized to default values IBM expected to be most useful for each mode. For instance, EGA 16-color modes initialize to the default CGA 16-color palette, and the 256-color mode initializes to a palette consisting of 16 CGA colors, 16 grey shades, and then 216 colors chosen by IBM to fit expected use cases.<ref>{{Cite book|url=http://classiccomputers.info/down/IBM_PS2/documents/PS2_Hardware_Interface_Technical_Reference_May88.pdf|title=IBM PS/2 Hardware Interface Technical Reference Manual|pages=13–18}}</ref><ref>[https://retrocomputing.stackexchange.com/questions/27994/why-were-those-colors-chosen-to-be-the-default-palette-for-256-color-vga retrocomputing SE question: why-were-those-colors-chosen-to-be-the-default-palette-for-256-color-vga ?]</ref>
After initialization they can be redefined at any time without altering the contents of video RAM, permitting [[Color cycling|palette cycling]].

In the 256-color modes, the DAC is set to combine four 2-bit color values, one from each plane, into an 8-bit-value representing an index into the 256-color palette. The CPU interface combines the 4 planes in the same way, a feature called "chain-4", so that each pixel appears to the CPU as a packed 8-bit value representing the palette index.<ref>Uphoff, Matthias (1990). ''Die Programmierung der EGA/VGA Grafikkarte''; {{ISBN|3-89319-274-3}}; this whole section was learned from this book</ref>
==Use==
The video memory of the VGA is mapped to the PC's memory via a window in the range between segments [[Hexadecimal|0xA0000]] and 0xBFFFF in the PC's [[real mode]] address space (A000:0000 and B000:FFFF in segment:offset notation). Typically, these starting segments are:

* 0xA0000 for EGA/VGA graphics modes (64&nbsp;[[Kibibyte|KB]])
* 0xB0000 for monochrome text mode (32&nbsp;KB)
* 0xB8000 for color text mode and CGA-compatible graphics modes (32&nbsp;KB)

A typical VGA card is also provides this port-mapped I/O segment:

* 0x3B0 to 0x3DF

Due to the use of different address mappings for different modes, it is possible to have a monochrome adapter (i.e. MDA or [[Hercules Graphics Card|Hercules]]) and a color adapter such as the VGA, [[Enhanced Graphics Adapter|EGA]], or [[Color Graphics Adapter|CGA]] installed in the same machine.

At the beginning of the 1980s, this was typically used to display [[Lotus 1-2-3]] spreadsheets in high-resolution text on a monochrome display and associated graphics on a low-resolution CGA display simultaneously. Many programmers also used such a setup with the monochrome card displaying debugging information while a program ran in graphics mode on the other card. Several debuggers, like Borland's [[Turbo Debugger]], [[D86 (debugger)|D86]] and Microsoft's [[CodeView]] could work in a dual monitor setup. Either Turbo Debugger or CodeView could be used to debug Windows.

There were also device drivers such as <code>ox.sys</code>, which implemented a serial interface simulation on the monochrome display and, for example, allowed the user to receive crash messages from debugging versions of Windows without using an actual serial terminal.

It is also possible to use the "MODE MONO" command at the command prompt to redirect the output to the monochrome display. When a monochrome adapter was not present, it was possible to use the 0xB000–0xB7FF address space as additional memory for other programs.

A VGA-capable [[PCI bus|PCI]] / [[PCI Express|PCIe]] graphics card can provide legacy VGA registers in its [[PCI configuration space]], which may be remapped by [[BIOS]] or [[operating system]].<ref>{{Cite web |title=PCI BARs and other means of accessing the GPU — envytools git documentation |url=https://envytools.readthedocs.io/en/latest/hw/bus/bars.html |access-date=2024-07-29 |website=envytools.readthedocs.io}}</ref>

=== 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.

==Hardware manufacturers==
Several companies produced VGA compatible graphic board models.<ref>{{cite web|url=http://www.techspot.com/article/650-history-of-the-gpu/|title=The History of the Modern Graphics Processor|website=techspot.com|access-date=6 May 2018|url-status=live|archive-url=https://web.archive.org/web/20160329140009/http://www.techspot.com/article/650-history-of-the-gpu/|archive-date=29 March 2016}}</ref>

*[[ATI Technologies|ATI]]: Graphics Solution Plus, Wonder series, Mach series
*[[S3 Graphics]]: S3 911, 911A, 924, 801, 805, 805i, 928, 805p, 928p, S3 Vision series, S3 Trio series
*[[Matrox]]: MAGIC RGB
*[[Plantronics]]: Colorplus
*[[Paradise Systems]]: PEGA 1, PEGA 1a, PEGA 2a
*[[Tseng Labs]]: ET3000, [[Tseng Labs ET4000|ET4000]], ET6000
*[[Cirrus Logic]]: CL-GD400, CL-GD500 and CL-GD5000 series
*[[Trident Microsystems]]: TVGA 8000 series, TVGA 9000 series, TGUI9000 series
*[[8x8|IIT]] 
*[[NEC]]
*[[Chips and Technologies]]
*[[Silicon Integrated Systems|SiS]]
*Tamerack
*[[Realtek]]
*[[Oak Technology]] 
*[[LSI Corporation|LSI]]
*Hualon
*Cornerstone Imaging 
*[[Winbond]]
*[[AMD]]
*[[Western Digital]] 
*[[Intergraph]]
*[[Texas Instruments]] 
*Gemini ([[List of defunct graphics chips and card companies|defunct]])
*[[Genoa Systems]] ([[List of defunct graphics chips and card companies|defunct]])

==Successors==
===Super VGA (SVGA)===
{{Main|Super VGA}}
Super VGA (SVGA) is a display standard developed in 1988, when [[NEC Home Electronics]] announced its creation of the [[Video Electronics Standards Association]] (VESA). The development of SVGA was led by [[NEC]], along with other VESA members including [[ATI Technologies]] and [[Western Digital]]. SVGA enabled [[graphics display resolution]]s up to 800&nbsp;×&nbsp;600 [[pixel]]s, 56% more than VGA's maximum resolution of 640&nbsp;×&nbsp;480 pixels.<ref name="InfoWorld 1988-11-14">{{cite news|title=NEC Forms Video Standards Group|first=Mark |last=Brownstein|work=[[InfoWorld]] |issn=0199-6649|date=November 14, 1988|volume=10 |issue=46 |page=3|access-date=May 27, 2016|url=https://books.google.com/books?id=wTsEAAAAMBAJ&pg=PT2}}</ref>

===Extended Graphics Array (XGA)===
{{Main|Extended Graphics Array}}

Extended Graphics Array (XGA) is an IBM display standard introduced in 1990. Later it became the most common appellation of the 1024&nbsp;×&nbsp;768 pixels [[display resolution]].

==See also==
*[[VGA text mode]]
*[[Graphic display resolutions]]
*[[List of color palettes]]
*[[List of video connectors]]
*[[List of monochrome and RGB color formats]]
*[[List of 16-bit computer hardware palettes]]
*[[List of defunct graphics chips and card companies]]
*[[Super VGA]]
*{{ill|AX-VGA|ja|Japanese Enhanced Graphics Adapter#AX-VGA}} (for Japanese [[AX architecture]] computers)
*[[DOS/V]]
*[[DisplayPort]] and [[HDMI]] (which have largely replaced VGA)

==References==
{{Reflist|30em}}

==Further reading==
*{{cite web|url=http://osdever.net./FreeVGA/vga/vga.htm|title=VGA Chipset Reference|work=Hardware Level VGA and SVGA Video Programming Information Page|author=J. D. Neal|year=1997}}
*{{Cite journal|url=http://playground.sun.com./1275/bindings/devices/html/vga-1_0d.html|title=CHRP VGA Display Device Binding to IEEE 1275–1994 Standard for Boot (Initialization, Configuration) Firmware|version=1.0|date=6 May 1996|author=Jordan Brown and John Kingman|access-date=22 June 2006|archive-url=https://web.archive.org/web/20060909014621/http://playground.sun.com/1275/bindings/devices/html/vga-1_0d.html|archive-date=9 September 2006|url-status=dead|df=dmy-all}}
*{{cite web|url=http://martin.hinner.info/vga/|title=VGA Interface and video signal documents|work= Signal Level VGA and SVGA Video Information Page|author=Hinner}}
*{{cite web|url=http://www.mcamafia.de/pdf/ibm_vgaxga_trm2.pdf|title=IBM VGA Technical Reference Manual|work=This is the original IBM reference. The document provides good overview of VGA functionality and is fairly complete, including a detailed description of standard BIOS modes and some programming techniques.}}

==External links==
{{commons category|VGA}}
*[http://pinouts.ru/Video/VGA15.shtml VGA pinout and signals descriptions]

{{Computer display standard}}
{{IBM personal computers}}
{{AVconn}}
{{Audio and video interfaces and connectors}}

[[Category:Products introduced in 1987]]
[[Category:Computer display standards]]
[[Category:American inventions]]
[[Category:IBM video hardware]]
[[Category:Analog communication interfaces]]
[[Category:Analog video connectors]]
[[Category:IBM PS/2]]