The term Video Graphics Array (VGA) refers specifically to the display hardware first introduced with the IBM PS/2 line of computers in 1987[1] , but through its widespread adoption has also come to mean either an analog computer display standard, the 15-pin D-subminiature VGA connector, or the 640×480 resolution itself. Analogue electronics (or analog in American English) are those electronic systems with a continuously Variable signal Various computer display standards or display modes have been used in the history of the Personal computer. The D-subminiature or D-sub is a common type of Electrical connector used particularly in Computers Calling them "subminiature" was appropriate A VGA connector as it is commonly known (other names include RGB connector D-sub 15 mini sub D15 and mini D15 is a three-row 15 pin DE-15. While this resolution has been superseded in the computer market, it is becoming a popular resolution on mobile devices[2]
VGA was the last graphical standard introduced by IBM that the majority of PC clone manufacturers conformed to, making it today (as of 2008) the lowest common denominator that all PC graphics hardware supports before a device-specific driver is loaded into the computer. A personal computer ( PC) is any Computer whose original sales price size and capabilities make it useful for individuals and which is intended to be operated 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. Splash screen is a term used to describe an Image that appears while a Computer program is loading
VGA was officially superseded by IBM's XGA standard, but in reality it was superseded by numerous slightly different extensions to VGA made by clone manufacturers that came to be known collectively as "Super VGA". XGA, the Extended Graphics Array, is an IBM display standard introduced in 1990. Super Video Graphics Array or Ultra Video Graphics Array, almost always abbreviated to Super VGA, Ultra VGA or just SVGA or UVGA is
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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. Motorola 6845 (commonly MC6845) is a video address generator first introduced by Motorola and used in the MDA, CGA and EGA video adapters Industry Standard Architecture (in practice almost always shortened to ISA) was a Computer bus standard for IBM compatible computers The Monochrome Display Adapter ( MDA, also MDA card, Monochrome Display and Printer Adapter, MDPA) introduced in 1981 was IBM The Color Graphics Adapter ( CGA) originally also called the Color/Graphics Adapter or IBM Color/Graphics Monitor Adapter The Enhanced Graphics Adapter (EGA is the IBM PC Computer display standard specification located between CGA and VGA in terms of graphics 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. A motherboard is the central or primary Printed circuit board (PCB making up a complex electronic system such as a modern Computer or Laptop A crystal oscillator is an Electronic circuit that uses the mechanical Resonance of a vibrating Crystal of piezoelectric material to create an Random Access Memory Digital-to-Analog Converter (RAMDAC is a combination of three fast DACs with a small SRAM used in computer graphics Display adapters The Personal System/2 or PS/2 was IBM 's third generation of Personal computers The PS/2 line released to the public in 1987 was created by IBM in an
The VGA specifications are as follows:
- 256 KB Video RAM
- 16-color and 256-color modes
- 262,144-value color palette (six bits each for red, green, and blue)
- Selectable 25. A kilobyte (derived from the SI prefix Kilo -, meaning 1000 is a unit of Information or Computer storage equal to either 1024 This is a list of color palettes of some of the most popular 16-bit Personal computers roughly those manufactured from 1985 to 1995. For a full listing of computer's color palettes see List of palettes This list of monochrome and RGB palettes includes 175 MHz [3] or 28. 3 MHz master clock
- Maximum of 720 horizontal pixels[4]
- Maximum of 480 lines[5]
- Refresh rates at up to 70 Hz [6]
- Vertical Blanking interrupt (Not all clone cards support this. In Digital imaging, a pixel ( pict ure el ement is the smallest piece of information in an image The hertz (symbol Hz) is a measure of Frequency, informally defined as the number of events occurring per Second. )
- Planar mode: up to 16 colors (4 bit planes)
- Packed-pixel mode: 256 colors (Mode 13h)
- Hardware smooth scrolling support
- Some "Raster Ops" support
- Barrel shifter
- Split screen support
- 0. Mode 13h is the IBM VGA BIOS mode number for a specific standard 256 color mode on IBM 's VGA graphics Hardware A barrel shifter is a Digital circuit that can shift a data word by a specified number of Bits in one Clock cycle. 7 V peak-to-peak
- 75 ohm impedance (9. The volt (symbol V) is the SI derived unit of electric Potential difference or Electromotive force. Amplitude is the magnitude of change in the oscillating variable with each Oscillation, within an oscillating system The ohm (symbol Ω) is the SI unit of Electrical impedance or in the Direct current case Electrical resistance, Electrical impedance, or simply impedance, describes a measure of opposition to a sinusoidal Alternating current (AC 3mA - 6. 5mW) [7][8]
The VGA supports both All Points Addressable graphics modes, and alphanumeric text modes. 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 Text mode is a kind of computer display mode in which the content of the screen is internally represented in terms of textual characters rather Standard graphics modes are
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 typically refers to the number of distinct pixels in each dimension that can be displayed Mode 13h is the IBM VGA BIOS mode number for a specific standard 256 color mode on IBM 's 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 The Color Graphics Adapter ( CGA) originally also called the Color/Graphics Adapter or IBM Color/Graphics Monitor Adapter The Monochrome Display Adapter ( MDA, also MDA card, Monochrome Display and Printer Adapter, MDPA) introduced in 1981 was IBM
The pinout can be found in the VGA connector page. A VGA connector as it is commonly known (other names include RGB connector D-sub 15 mini sub D15 and mini D15 is a three-row 15 pin DE-15.
Standard text modes
Standard alphanumeric text modes for the VGA use 80×25 or 40×25 text cells. Text mode is a kind of computer display mode in which the content of the screen is internally represented in terms of textual characters rather 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.
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. 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 bit field This byte-pair scheme is among the features that VGA inherited ultimately from CGA.
The VGA color palette
- See also the List of monochrome and RGB palettes article — 18-bit RGB section, and the List of 16-bit computer hardware palettes article — MCGA and VGA section. For a full listing of computer's color palettes see List of palettes This list of monochrome and RGB palettes includes For a full listing of computer's color palettes see List of palettes This list of monochrome and RGB palettes includes This is a list of color palettes of some of the most popular 16-bit Personal computers roughly those manufactured from 1985 to 1995. This is a list of color palettes of some of the most popular 16-bit Personal computers roughly those manufactured from 1985 to 1995.
The VGA color system is backwards compatible with the EGA and CGA adapters, and adds another level of configuration on top of that. The Enhanced Graphics Adapter (EGA is the IBM PC Computer display standard specification located between CGA and VGA in terms of graphics The Color Graphics Adapter ( CGA) originally also called the Color/Graphics Adapter or IBM Color/Graphics Monitor Adapter CGA was able to display up to 16 colors, and 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). For a full listing of computer's color palettes see List of palettes This is a list of color palettes of some of the This is a list of color palettes of some of the most popular 16-bit Personal computers roughly those manufactured from 1985 to 1995. For a full listing of computer's color palettes see List of palettes This list of monochrome and RGB palettes includes VGA further extends this scheme by increasing the EGA palette from 64 entries to 256 entries. Two more blocks of 64 colors with progressively darker shades were added, along with 8 "blank" entries that were set to black. [9]
In addition to the extended palette, each of the 256 entries could be assigned an arbitrary color value through the VGA DAC. 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 The EGA BIOS only allowed 2 bits per channel to represent each entry, while VGA allowed 6 bits to represent the intensity of each of the three primaries (red, blue and green). This provided 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 allowed 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 is the IBM VGA BIOS mode number for a specific standard 256 color mode on IBM 's 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 0xA0000 and 0xC0000 in the PC's real mode address space. Real mode, also called real address mode, is an operating mode of 80286 and later X86 -compatible CPUs. Typically these starting segments are:
- 0xA0000 for EGA/VGA graphics modes (64 KB)
- 0xB0000 for monochrome text mode (32 KB)
- 0xB8000 for color text mode and CGA-compatible graphics modes (32 KB)
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. A kilobyte (derived from the SI prefix Kilo -, meaning 1000 is a unit of Information or Computer storage equal to either 1024 The Monochrome Display Adapter ( MDA, also MDA card, Monochrome Display and Printer Adapter, MDPA) introduced in 1981 was IBM The Enhanced Graphics Adapter (EGA is the IBM PC Computer display standard specification located between CGA and VGA in terms of graphics 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. The 1980s was the decade spanning from January 1 1980 to December 31 1989. Lotus 1-2-3 is a Spreadsheet program from Lotus Software (now part of IBM) 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. Turbo Debugger was a machine-level debugger for MS-DOS executables sold by Borland. Cox) and Microsoft's CodeView could work in a dual monitor setup. CodeView was a standalone Debugger created by David Norris at Microsoft in 1985 as part of its development toolset 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. DOS, short for "Disk Operating System" is a shorthand term for several closely related Operating systems that dominated the IBM PC compatible market 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. High Memory is the part of physical memory in a Computer which is not directly mapped by the page tables of its Operating system kernel )
Programming tricks
An undocumented but popular technique nicknamed Mode X (first coined by Michael Abrash) or "tweaked VGA" was used to make programming techniques and graphics resolutions available that were not otherwise possible in the standard Mode 13h. Mode X is an alternative video graphics display mode of the IBM VGA graphics hardware that was popularized by Michael Abrash, first published in July 1991 Michael Abrash is a highly regarded Technical writer, and one of the top optimization and 80x86 This was done by "unchaining" the 256 KB VGA memory into four separate "planes", which would make all of VGA's 256 KB 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:
- 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.
- Several higher-resolution display modes were possible: at 16 colors, 704×528, 736×552, 768×576, and even 800×600 were possible. Software such as Xlib (a VGA graphics library for C in the early 1990s) and ColoRIX (a 256-color graphics program), also supported tweaked 256-color modes using many combinations of columns of 256, 320, and 360 pixels, and rows of 200, 240, 256, 400, and 480 lines (the upper limit being 640×400 which used almost every available byte of VGA's 256 KB video ram). However, 320×240 was the best known and most-frequently used since it was a typical 4:3 aspect ratio resolution with square pixels.
- The use of multiple video pages in hardware allowed the programmer to perform double buffering or triple buffering, which, while available in VGA's 320×200 16-color mode, was not possible using stock Mode 13h. In Computer science, double buffering (or ping-pong buffering is a widely used technique for minimizing the delay (flicker in Input/output operations which In Computer graphics, triple buffering is a variant on Double buffering, a technique for drawing graphics that shows no (or less flicker shearing and tearing artifacts Mode 13h is the IBM VGA BIOS mode number for a specific standard 256 color mode on IBM 's VGA graphics Hardware
Sometimes the monitor refresh rate had to be reduced to accommodate these modes, increasing eye-strain. The refresh rate (most commonly the "vertical refresh rate" "vertical scan rate" for CRTs is the number of times in a second that display hardware draws 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 320×240 (square pixels, three video pages), 320×400 (double resolution, two video pages), and 360×480 (highest resolution compatible with standard VGA monitors, one video page).
Comparison chart
| Name | x (width) |
y (height) |
Pixels (x1 Million) |
Aspect Ratio |
Percentage of difference in pixels | Widescreen Version |
Typical screen sizes |
|||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| VGA | SVGA | XGA | XGA+ | SXGA | SXGA+ | UXGA | QXGA | |||||||
| VGA | 640 | 480 | 0. The term Video Graphics Array ( VGA) refers specifically to the display hardware first introduced with the IBM PS/2 line of computers in 1987, but through its widespread 31 | 1. 33 | 0% | -36% | -61% | -69% | -77% | -79% | -84% | -90% | WVGA | |
| SVGA | 800 | 600 | 0. Wide VGA or WVGA is any Display resolution wider than VGA, eg Super Video Graphics Array or Ultra Video Graphics Array, almost always abbreviated to Super VGA, Ultra VGA or just SVGA or UVGA is 48 | 1. 33 | 56% | 0% | -39% | -52% | -63% | -67% | -75% | -85% | ||
| XGA | 1024 | 768 | 0. XGA, the Extended Graphics Array, is an IBM display standard introduced in 1990. 79 | 1. 33 | 156% | 64% | 0% | -21% | -40% | -47% | -59% | -75% | WXGA | 15"/ 38cm |
| XGA+ | 1152 | 864 | 1. Comparison chart WQUXGA display - 3840 x 2400 pixels (commercially available since Nov 2007 XGA+ stands for eXtended Graphics Array Plus and is a Computer display standard. 00 | 1. 33 | 224% | 107% | 27% | 0% | -24% | -32% | -48% | -68% | WXGA+ | 17"/ 43cm |
| SXGA | 1280 | 1024 | 1. WSXGA and WXGA+ are non-standard terms referring to computer display resolutions SXGA is an acronym for Super eXtended Graphics Array referring to a standard monitor resolution of 1280×1024 Pixels This Display resolution 31 | 1. 25 | 327% | 173% | 67% | 32% | 0% | -11% | -32% | -58% | WSXGA | 17-19"/ 43-48cm |
| SXGA+ | 1400 | 1050 | 1. WSXGA and WXGA+ are non-standard terms referring to computer display resolutions SXGA+ stands for Super eXtended Graphics Array Plus and is a Computer display standard. 47 | 1. 33 | 379% | 206% | 87% | 48% | 12% | 0% | -23% | -53% | WSXGA+ | |
| UXGA | 1600 | 1200 | 1. WSXGA+ stands for W idescreen S uper e' X' tended G raphics A rray and is a Computer display standard. UXGA is an abbreviation for Ultra eXtended Graphics Array referring to a standard monitor resolution of 1600 × 1200 Pixels which is exactly 92 | 1. 33 | 525% | 300% | 144% | 93% | 46% | 31% | 0% | -39% | WUXGA | 20"/ 51cm |
| QXGA | 2048 | 1536 | 3. WUXGA stands for Widescreen Ultra eXtended Graphics Array and is a Display resolution of 1920×1200 Pixels (2304000 pixels with a 1610 screen The QXGA, or Quad eXtended Graphics Array, display standard is a resolution standard in display technology 15 | 1. 33 | 924% | 555% | 300% | 216% | 140% | 114% | 64% | 0% | WQXGA | 30"/ 76cm |
See also
- Digital Visual Interface (DVI), the digital equivalent
- List of display interfaces
- List of monochrome and RGB palettes — 18-bit RGB section
- List of 16-bit computer hardware palettes — MCGA and VGA section
References
- ^ Chronology of IBM Personal Computers. The QXGA, or Quad eXtended Graphics Array, display standard is a resolution standard in display technology The Digital Visual Interface ( DVI) is a Video interface standard designed to maximize the visual quality of digital Display devices such as Flat panel This is a list of physical video connectors and related video signal standards. For a full listing of computer's color palettes see List of palettes This list of monochrome and RGB palettes includes For a full listing of computer's color palettes see List of palettes This list of monochrome and RGB palettes includes This is a list of color palettes of some of the most popular 16-bit Personal computers roughly those manufactured from 1985 to 1995. This is a list of color palettes of some of the most popular 16-bit Personal computers roughly those manufactured from 1985 to 1995.
- ^ Windows Mobile 6 phone boasts VGA display.
- ^ VGA 640x350 Signal timing.
- ^ PS/2 Video Subsystem Technical Reference Manual 1992
- ^ PS/2 Video Subsystem Technical Reference Manual 1992
- ^ VGA Signal timings.
- ^ Q: VGA video signal specs sci.electronics. 070731 groups. google. com
- ^ ePanorama.net - Circuits. 070731 epanorama. net
- ^ Norton, Peter and Wilton, Richard (1988). Peter Norton (born November 14 1943) is an American Software Publisher, Author, and Philanthropist. The new Peter Norton programmer's guide to the IBM PC and PS/2.
Further reading
- J. D. Neal (1997). VGA Chipset Reference. Hardware Level VGA and SVGA Video Programming Information Page.
- Jordan Brown and John Kingman (1996-05-06). Year 1996 ( MCMXCVI) was a Leap year starting on Monday (link will display full 1996 Gregorian calendar) Events 1527 - Spanish and German troops sack Rome; some consider this the end of the Renaissance. "CHRP VGA Display Device Binding to IEEE 1275-1994 Standard for Boot (Initialization, Configuration) Firmware". 1. 0.
- Hinner. VGA Interface and video signal documents. Signal Level VGA and SVGA Video Information Page.
External links
Dapyx Software network: MP3 Explorer | Ebook Manager | Zenithic