NationMaster - Encyclopedia: Video Graphics Array

Video Graphics Array (VGA) is an analog computer display standard first marketed in 1987 by IBM. It has been technologically outdated in the PC market for some time. VGA was the most recent graphical standard that the majority of manufacturers conformed to, making it the lowest common denominator that all PC graphics hardware supports before a device-specific driver is loaded into the computer. For example, the Microsoft Windows splash screen appears while the machine is still operating in VGA mode, which is the reason that this screen always appears in reduced resolution and color depth. Image File history File linksMetadata Size of this preview: 800 Ã— 600 pixels Full resolution (1056 Ã— 792 pixel, file size: 303 KB, MIME type: image/jpeg) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Video Graphics Array Metadata This... Image File history File linksMetadata Size of this preview: 800 Ã— 600 pixels Full resolution (1056 Ã— 792 pixel, file size: 303 KB, MIME type: image/jpeg) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Video Graphics Array Metadata This... Image File history File linksMetadata Size of this preview: 800 Ã— 600 pixels Full resolution (1056 Ã— 792 pixel, file size: 194 KB, MIME type: image/jpeg) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Video Graphics Array Metadata This... Image File history File linksMetadata Size of this preview: 800 Ã— 600 pixels Full resolution (1056 Ã— 792 pixel, file size: 194 KB, MIME type: image/jpeg) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Video Graphics Array Metadata This... Wikipedia does not yet have an article with this exact name. ... Various computer display standards or display modes have been used in the history of the personal computer. ... 1987 (MCMLXXXVII) was a common year starting on Thursday of the Gregorian calendar. ... International Business Machines Corporation (known as IBM or Big Blue; NYSE: IBM) is a multinational computer technology and consulting corporation headquartered in Armonk, New York, USA. The company is one of the few information technology companies with a continuous history dating back to the 19th century. ... The Altair 8800 was among the first microcomputers to be affordable by an individual, although it initially lacked peripherals and memory. ... A splash screen in Inkscape with the logo and version information Splash screen is a term used to describe an image that appears while a computer program is loading. ...

The term VGA is often used to refer to a resolution of 640×480, regardless of the hardware that produces the picture (even though this resolution is outdated in PC, in the pocket PC / PDA market it is currently becoming the standard). It may also refer to the 15-pin D-subminiature VGA connector which is still widely used to carry analog video signals of all resolutions. It has been suggested that DE-9 be merged into this article or section. ... VGA Connector There are at least four versions of VGA connector, the three-row 15 pin DE-15 (also called mini sub D15) in originaland DDC2pinouts, and a less featureful and far less common 9-pin VGA, plus a Mini-VGA used for laptops. ...

VGA was officially superseded by IBM's XGA standard, but in reality it was superseded by numerous extensions to VGA made by clone manufacturers that came to be known as "Super VGA". XGA, the eXtended Graphics Array, is an IBM display standard introduced in 1990. ... The Jargon File has this definition for clone: An exact duplicate: Our product is a clone of their product. ... Super Video Graphics Array, almost always abbreviated to Super VGA or just SVGA is a broad term that covers a wide range of computer display standards. ...

Technical details

VGA is referred to as an "array" instead of an "adapter" because it was implemented from the start as a single chip, replacing the Motorola 6845 and dozens of discrete logic chips covering a full-length ISA board that the MDA, CGA, and EGA used. This also allowed it to be placed directly on a PC's motherboard with a minimum of difficulty (it only required video memory, timing crystals and an external RAMDAC), and the first IBM PS/2 models were equipped with VGA on the motherboard. The Motorola 6845 (commonly MC6845) is a video address generator first introduced by Motorola and used in the CGA and EGA video adapters, Amstrad CPC and BBC Micro. ... This article or section does not adequately cite its references or sources. ... Green screen driven by a Monochrome Display Adapter The Monochrome Display Adapter (MDA, also MDA card, Monochrome Display and Printer Adapter, MDPA) introduced in 1981 was IBMs standard video display card and computer display standard for the PC. The MDA did not have any graphics mode of any kind... The Color Graphics Adapter (CGA), introduced in 1981, was IBMs first color graphics card, and the first color computer display standard for the IBM PC. The standard IBM CGA graphics card was equipped with 16 kilobytes of video memory. ... The Enhanced Graphics Adapter (EGA) is the IBM PC computer display standard specification located between CGA and VGA in terms of graphics performance (that is, colour and space resolution). ... A motherboard is the central or primary circuit board making up a complex electronic system, such as a modern computer. ... A crystal oscillator is an electronic device that uses the mechanical resonance of a physical crystal of piezoelectric material to create an electrical signal with a very precise frequency. ... Random Access Memory Digital-to-Analog Converter is a combination of three fast DACs with a small SRAM used in graphics display adapters to store the color palette and to generate the analog signals (usually a voltage amplitude) to drive a colour monitor. ... The Personal System/2 or PS/2 was IBMs second generation of personal computers. ...

The VGA supports both All Points Addressable graphics modes, and alphanumeric text modes. Standard graphics modes are A kibibyte (a contraction of kilo binary byte) is a unit of information or computer storage, commonly abbreviated KiB (never kiB). 1 kibibyte = 210 bytes = 1,024 bytes The kibibyte is closely related to the kilobyte, which can be used either as a synonym for kibibyte or to refer to... Random access memory (usually known by its acronym, RAM) is a type of data storage used in computers. ... This example shows an image with a portion greatly enlarged, in which the individual pixels are rendered as little squares and can easily be seen. ... The hertz (symbol: Hz) is the SI unit of frequency. ... Mode 13h (the h here stands for hexadecimal, so this is actually VGA mode 19) is a standard 256 colour mode on IBMs VGA graphics hardware. ... Suppose the smiley face in the top left corner is an RGB bitmap image. ... A barrel shifter is a digital circuit that can shift a data word by any number of bits in a single cycle. ... For the origin and evolution of fonts, see History of western typography. ... All Points Addressable (APA), in the context of a video monitor, dot matrix or any display device consisting of a pixel array, refers to an arrangement bits or cells which can be individually manipulated, as opposed to rewriting the whole array every time a pixel changes. ... A text mode program communicates with the user by only displaying text and possibly a limited set of predefined semi-graphical characters, which allow the drawing of rudimentary boxes around portions of text, either to highlight the content or to simulate widget or control interface objects found in GUI programs. ...

As well as the standard modes, VGA can be configured to emulate many of the modes of its predecessors (EGA, CGA, and MDA). The display resolution of a digital television or computer display is the number of pixels (or maximal image resolution) that can be displayed on the screen, usually given as a product of the number of columns (horizontal, X) is always stated first and the number or rows (vertical, Y) make... Mode 13h (the h here stands for hexadecimal, so this is actually VGA mode 19) is a standard 256 colour mode on IBMs VGA graphics hardware. ... The Enhanced Graphics Adapter (EGA) is the IBM PC computer display standard specification located between CGA and VGA in terms of graphics performance (that is, colour and space resolution). ... The Color Graphics Adapter (CGA), introduced in 1981, was IBMs first color graphics card, and the first color computer display standard for the IBM PC. The standard IBM CGA graphics card was equipped with 16 kilobytes of video memory. ... Green screen driven by a Monochrome Display Adapter The Monochrome Display Adapter (MDA, also MDA card, Monochrome Display and Printer Adapter, MDPA) introduced in 1981 was IBMs standard video display card and computer display standard for the PC. The MDA did not have any graphics mode of any kind...

Standard text modes

Standard alphanumeric text modes for the VGA use 80×25 or 40×25 text cells. Each cell may choose from one of 16 available colors for its foreground and 8 colors for the background; the 8 background colors allowed are the ones without the high-intensity bit set. Each character may also be made to blink; all that are set to blink will blink in unison. The blinking option for the entire screen can be exchanged for the ability to choose the background color for each cell from among all 16 colors. All of these options are the same as those on the CGA adapter as introduced by IBM. A text mode program communicates with the user by only displaying text and possibly a limited set of predefined semi-graphical characters, which allow the drawing of rudimentary boxes around portions of text, either to highlight the content or to simulate widget or control interface objects found in GUI programs. ...

VGA adapters usually support both a monochrome and a color text mode, though the monochrome mode is almost never used. Black and white text on nearly all modern VGA adapters is drawn by using gray colored text on a black background in color mode. VGA monochrome monitors were sold (intended primarily for text applications), but most of them will work at least adequately with a VGA adapter in color mode. Occasionally a faulty connection between a modern monitor and video card will cause the VGA part of the card to detect the monitor as monochrome, and this will cause the BIOS and initial boot sequence to appear in greyscale. Usually once the video card's drivers are loaded (for example by continuing to boot into the operating system) they will override this detection and the monitor will return to color.

In color text mode, each screen character is actually represented by two bytes. The lower, or character byte is the actual character for the current character set, and the higher, or attribute byte is a bit field used to select various video attributes such as color, blinking, character set, and so forth. This byte-pair scheme is among the features that VGA inherited ultimately from CGA. A bit field is a common idiom used in computer programming to store a set of Boolean datatype flags compactly, as a series of bits. ...

The VGA color palette

The VGA color system is backwards compatible with the EGA and CGA adapters, and adds another level of configuration on top of that. The CGA was able to display up to 16 colors, and the EGA extended this by allowing each of the 16 colors to be chosen from a 64-color palette (these 64 colors are made up of two bits each for red, green and blue: two bits × three channels = six bits = 64 different values.) The VGA further extends this scheme by increasing the EGA palette from 64 entries to 256 entries, but in order to retain backwards compatibility only 64 entries out of the full 256 can be selected at any one time, in blocks of 64 (i.e. the first 64 entries, or the second 64, etc.) This allows for four complete EGA palettes to be stored in the VGA hardware at the same time, and it is possible to rapidly switch between each of these palettes allowing the colors on the screen to be changed almost instantly.^[1] The Enhanced Graphics Adapter (EGA) is the IBM PC computer display standard specification located between CGA and VGA in terms of graphics performance (that is, colour and space resolution). ... The Color Graphics Adapter (CGA), introduced in 1981, was IBMs first color graphics card, and the first color computer display standard for the IBM PC. The standard IBM CGA graphics card was equipped with 16 kilobytes of video memory. ...

In addition to the extended 256-entry EGA-style palette, each of the 256 entries can be assigned an arbitrary color value through the VGA DAC. This changed the purpose of the EGA palette somewhat, as under the EGA it was a method of choosing any possible color using only two bits per channel, but under the VGA it becomes a simple 64-entry lookup table, whose values can be arbitrarily changed - the entries can easily be changed so they no longer reflect the EGA system where the lower two bits in the index represent the amount of red in the color. In electronics, a digital-to-analog converter (DAC or D-to-A) is a device for converting a digital (usually binary) code to an analog signal (current, voltage or electric charge). ... In computer science, a lookup table is a data structure, usually an array or associative array, used to replace a runtime computation with a simpler lookup operation. ...

The VGA scheme used six bits per channel (up from the EGA's two bits per channel) when changing an entry in the palette, providing a total of 63 different intensity levels for red, green and blue, resulting in 262,144 possible colors, any 256 of which could be assigned to the palette (and in turn out of those 256, any 16 of them could be displayed in CGA video modes.)

This method did however allow new VGA colors to be used in EGA and CGA graphics modes, providing one remembered how the different palette systems are laid together - to set the text color to very dark red in text mode for instance, it will need to be set to one of the CGA colors (for example the default color #7, light grey.) This color then maps to one in the EGA palette - in the case of CGA color 7, it maps to EGA palette entry 42. The VGA DAC must then be configured to change color 42 to dark red, and then immediately anything displayed on the screen in light-grey (CGA color 7) will become dark red. This feature was often used in 256-color VGA DOS games when they first loaded, by smoothly fading out the text screen to black.

While CGA and EGA compatible modes only allowed 16 colors to be displayed at any one time, other VGA modes such as the widely used mode 13h allowed all 256 palette entries to be displayed on the screen at the same time, and so in these modes any 256 colors could be shown out of the 262,144 colors available. Mode 13h (the h here stands for hexadecimal, so this is actually VGA mode 19) is a standard 256 colour mode on IBMs VGA graphics hardware. ...

Addressing details

The video memory of the VGA is mapped to the PC's memory via a window in the range between segments 0xA000 and 0xC000 in the PC's real mode address space. Typically these starting segments are: Real mode (also called real address mode in Intels manuals) is an operating mode of 80286 and later x86-compatible CPUs. ...

Due to the use of different address mappings for different modes, it is possible to have a Monochrome Display Adapter and a color adapter such as the VGA, EGA, or 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 MDA 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 (by Alan J. Cox) 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 DOS device drivers such as ox.sys, which implemented a serial interface simulation on the MDA 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 DOS prompt to redirect the output to the monochrome display. When a Monochrome Display Adapter was not present it was possible to use the 0xB000 - 0xB7FF address space as additional memory for other programs (for example by adding the line "DEVICE=EMM386.EXE I=B000-B7FF" into config.sys, this memory would be made available to programs that can be "loaded high" - loaded into high memory.) A kibibyte (a contraction of kilo binary byte) is a unit of information or computer storage, commonly abbreviated KiB (never kiB). 1 kibibyte = 210 bytes = 1,024 bytes The kibibyte is closely related to the kilobyte, which can be used either as a synonym for kibibyte or to refer to... Green screen driven by a Monochrome Display Adapter The Monochrome Display Adapter (MDA, also MDA card, Monochrome Display and Printer Adapter, MDPA) introduced in 1981 was IBMs standard video display card and computer display standard for the PC. The MDA did not have any graphics mode of any kind... EGA may stand for Enhanced Graphics Adapter Éléments de géométrie algébrique. ... CGA may stand for: Certified General Accountant Color Graphics Adapter This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same title. ... This article cites very few or no references or sources. ... Lotus 1-2-3 is a spreadsheet program from Lotus Software (now part of IBM). ... This page meets Wikipedias criteria for speedy deletion. ... A86 is a compact commercial assembler developed for the Intel x86 family of microprocessors by Eric Issacson. ... CodeView was a standalone debugger created by Microsoft as part of its development toolset. ... Instructions on how to use the directory command. ... The High Memory Area (HMA) is the RAM area consisting of the first 64 kilobytes (KB), minus 16 bytes, of the extended memory on an IBM PC or compatible microcomputer. ...

Programming tricks

An undocumented but popular technique nicknamed Mode X (first coined by Michael Abrash) was used to make available programming techniques and graphics resolutions not possible in the standard Mode 13h. This was done by "unchaining" the 256 KiB VGA memory into four separate "planes", which would make all of VGA's 256 KiB of RAM available in 256-color modes. There was a trade-off for extra complexity and performance loss in some types of graphics operations, but this was mitigated by other operations becoming faster in certain situations: Mode X is an undocumented video graphics display mode of the IBM VGA graphics hardware that was popularized by Michael Abrash, first published in July 1991 in Dr. Dobbs Journal, republished in chapters 47-49 of Abrashs Graphics Programming Black Book, which is now freely available online in... Michael Abrash is best known as a technical writer and one of the top optimization and 80x86 assembly language programmers, a reputation cemented by his 1990 book Unfortunately, the original 8086 processor, the focus of the book, was several generations behind the state of the art by the time the...

Sometimes the monitor refresh rate had to be reduced to accommodate these modes, increasing eye-strain. They were also incompatible with some older monitors, producing display problems such as picture detail disappearing into overscan, flickering, vertical roll, and lack of horizontal sync depending on the mode being attempted. Because of this, most VGA tweaks used in commercial products were limited to "monitor-safe" combinations, such as 320×400 (double resolution, two video pages), 320×240 (square pixels, three video pages), and 360x480 (highest resolution compatible with standard VGA monitors, one video page). In computer graphics, double buffering (sometimes called ping-pong buffering) is a technique used to reduce or remove visible artifacts from the drawing process. ... Mode 13h (the h here stands for hexadecimal, so this is actually VGA mode 19) is a standard 256 colour mode on IBMs VGA graphics hardware. ... The refresh rate (or vertical refresh rate, vertical scan rate for CRTs) is the number of times in a second that a display is illuminated. ...

References

Peter Norton Peter Norton (born November 14, 1943) is an American software publisher and philanthropist. ...

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