The Enhanced Graphics Adapter (EGA) is an IBM PCgraphics adapter[2][3] and de factocomputer display standard from 1984 that superseded the CGA standard introduced with the original IBM PC, and was itself superseded by the VGA standard in 1987. In addition to the original EGA card manufactured by IBM, many compatible third-party cards were manufactured, and EGA graphics modes continued to be supported by VGA and later standards.
EGA was introduced in October 1984 by IBM,[2][3] shortly after its new PC/AT. The EGA could be installed in previously released IBM PCs, but required a ROM upgrade on the mainboard.[4]
Chips and Technologies' first product, announced in September 1985, was a four-chip EGA chipset that handled the functions of 19 of IBM's proprietary chips on the original Enhanced Graphics Adapter. By that November's COMDEX, more than a half dozen companies had announced EGA-compatible boards based on C&T's chipset.[5] The first EGA-compatible board was Vega in December 1985, released by Video Seven and using C&T's chipset.[6]:34 The Vega was half the width of the original IBM EGA board.[7]
Between 1984 and 1987, several third-party manufacturers produced compatible cards, such as the Autoswitch EGA[8] or Genoa Systems' Super EGA chipset.[9] Later cards supporting an extended version of the VGA were similarly named Super VGA.
The EGA standard was made obsolete in 1987 by the introduction of MCGA and VGA with the PS/2 computer line.[10]
By 1987, EGA support was commonplace.[17] Most software made up to 1991 could run in EGA, although the vast majority of commercial games used 320 × 200 with 16 colors for backwards compatibility with CGA and Tandy, and to support users who did not own an enhanced EGA monitor. 350-line modes were mostly used by freeware/shareware games and application software, although SimCity is a notable example of a commercial game that runs in 640 × 350 with 16 colors mode.[18][19]
Hardware design
IBM MDA, CGA and EGA monitors, all supported by the EGA card
The original IBM EGA was an 8-bit PC ISA card with 64KB of onboard RAM. An optional daughter-board (the Graphics Memory Expansion Card) provided a minimum of 64KB additional RAM, and up to 192 KB if fully populated with the Graphics Memory Module Kit.[20] Without these upgrades, the card would be limited to four colors in 640×350 mode.[21]
Output was via direct-drive RGB,[22] as with the CGA, but no composite video output was included.[23] MDA and CGA monitors could be driven, as well as newly released enhanced color monitors for use specifically with EGA.[24]
EGA-specific monitors used a dual-sync design which could switch from the 15.7kHz of 200-line modes to 21.8kHz for 350-line modes.[24]
A non-IBM EGA card
Many EGA cards have DIP switches on the back of the card to select the monitor type. If CGA is selected, the card will operate in 200-line mode and use 8×8 characters in text mode. If EGA is selected, the card will operate in 350-line mode and use 8×14 text.
Some third-party cards using the EGA specification were sold with the full 128KB of RAM from the factory, while others included as much as 256KB to enable multiple graphics pages, multiple text-mode character sets, and large scrolling displays.[8] A few third-party cards, such as the ATI TechnologiesEGA Wonder, built on the EGA standard to additionally offer features such as extended graphics modes as high as 800 × 560 and automatic monitor type detection.[25]
Capabilities
EGA produces a display of up to 16 colors (using a fixed palette, or one selected from a gamut of 64 colors (6-bit RGB), depending on mode) at several resolutions up to 640×350 pixels, as well as two monochrome modes at higher resolutions. EGA cards include a ROM to extend the system BIOS for additional graphics functions, and a custom CRT controller (CRTC).[26]
The IBM EGA CRTC supports all of the modes of the IBM MDA and CGA adapters through specific mode options,[26] but it is not fully register-compatible with the MotorolaMC6845 used in those cards, so software that directly programs the registers to select modes may produce different results on the EGA.[27]
Supported resolutions are 320×200 and 640×200 (on a CGA or EGA monitor[28]), 720×350 and 640×350 (on an MDA monitor) and 320×350 and 640×350 (on an EGA monitor). EGA scans at 21.8kHz when 350-line modes are used and 15.7kHz when 200-line modes are used.[24]
In the 640×350 high-resolution mode, which requires an enhanced EGA monitor, 16 colors can be selected from a palette comprising all combinations of two bits per pixel for red, green and blue. This is four levels of intensity for each primary color and 64 colors overall. The 640×200 and 320×200 graphics modes provide backwards compatibility with CGA software and monitors, but they can use the entire sixteen-color CGA palette simultaneously, instead of the smaller four-color palettes that the actual CGA is limited to in those modes.[28]
Screenshot of the Arachne web browser using the 640 × 350 graphics mode. The screenshot contains 14 colors.
Modes
EGA supports:
640 × 350×16 colors (from a 6bit palette of 64 colors), pixel aspect ratio of 1:1.37.
640 × 350×2 colors, pixel aspect ratio of 1:1.37.
640 × 200×16 colors, pixel aspect ratio of 1:2.4.
320 × 200×16 colors, pixel aspect ratio of 1:1.2.
Text modes:
40 × 25 with 8×8 pixel font (effective resolution of 320 × 200)
80 × 25 with 8×8 pixel font (effective resolution of 640 × 200)
80 × 25 with 8×14 pixel font (effective resolution of 640 × 350)
80 × 43 with 8×8 pixel font (effective resolution of 640 × 344)
Extended graphics modes of third-party boards:[citation needed]
640 × 400
640 × 480
720 × 540
800 × 560
Color palette
With the EGA, all 16 CGA colors can be used simultaneously, and each can be mapped in from a larger palette of 64 colors (two bits each for red, green and blue). The CGA's alternate brown color is included in the larger palette, so it can be used without any additional display hardware. The later VGA standard built on this by mapping each of the 64 colors in from a larger, customizable, palette of 256.
Standard EGA monitors do not support use of the extended color palette in 200-line modes, because the monitor cannot distinguish between being connected to a CGA card or being connected to an EGA card outputting a 200-line mode. EGA redefines some pins of the connector to carry the extended color information. If the monitor were connected to a CGA card, these pins would not carry valid color information, and the screen might be garbled if the monitor were to interpret them as such. For this reason, standard EGA monitors will use the CGA pin assignment in 200-line modes, so the monitor can also be used with a CGA card.[citation needed]
Some EGA monitors are switchable, meaning that they can be set up to use the full palette even in 200-line modes, often through a mechanical switch. Only a few commercial games were released with support for the extended color palette in 320 × 200 or 640 × 200 (including the DOS version of Super Off Road).[31][32]
When selecting a color from the EGA palette, two bits are used for the red, green and blue channels to signal values of 0, 1, 2 or 3. For instance, to select the color magenta, the red and blue values would be medium intensity (2, or 10 in binary) and the green value would be off (0).
The table below displays an example palette matching the standard 16 CGA colors, with their representations in rgbRGB binary (internal card bit order), where the lowercase letters are the low-intensity bits, and uppercase letters are high-intensity bits. Decimal and hexadecimal values (converted to equivalent 24-bitsRGBweb colors) are also shown.
The following images illustrate the full EGA palette in detail.
Full 64-color EGA palette table
Full 64-color EGA palette illustration
Full 64-color EGA palette test card
Screen color test with custom EGA palette
Specifications
EGA connector pinout when looking at back of computer
EGA uses a female nine-pin D-subminiature (DE-9) connector for output, identical to the CGA connector. The signal standard and pinout is backwards-compatible with CGA, allowing EGA monitors to be used on CGA cards and conversely.
When operating in EGA modes, pins 2, 6 and 7 are repurposed for EGA's secondary RGB signals (see pinout table below). When operating in 200-line CGA modes, the EGA card is fully backwards compatible with a standard IBM CGA monitor; however, third-party monitors had varying compatibility.[citation needed]
Front and rear views of the TVM MD-3, a third-party EGA monitor. DE-9 input, mode switch, contrast and brightness controls at front, Vsize and Vhold knobs at rear.
Third-party monitors sometimes connected pin two to ground internally. When connected to an EGA card, this shorts the EGA's secondary red output to ground and can damage the card. Also, some monitors were wired with pin two as their sole ground, and these will not work with the EGA.[citation needed]
Conversely, an EGA monitor should work with a CGA adapter, but if it is not set to CGA mode, the secondary red signal will be grounded (always zero), and the secondary blue will be floating (unconnected), causing all high-intensity colors except brown to display incorrectly, and all colors to potentially have a variable blue tint due to the indeterminate state of the unconnected secondary blue.[citation needed]
The IBM 5154 EGA monitor has a special IBM 5153 CGA compatibility mode when operating with CGA sync signals and automatically changes to the CGA pinout to avoid all of the mentioned problems when operating in this mode.[33]
EGA DE-9 connector pin signals
Pin
Name
EGA modes
CGA compatible modes
1
GND
Ground
Ground
2
SR
Secondary Red (Intensity)
Ground
3
PR
Primary Red
Red
4
PG
Primary Green
Green
5
PB
Primary Blue
Blue
6
SG
Secondary Green (Intensity)
Intensity
7
SB
Secondary Blue (Intensity)
Reserved
8
H
Horizontal sync
Horizontal sync
9
V
Vertical sync
Vertical sync
The original IBM EGA card includes a feature connector (blue connector J4, see first photo on this page), providing access to two RCA connectors at the back of card, in addition to several analog and digital signals that the EGA adaptor can be configured to use.[34]
A light pen interface was also present on the original card.[35]
Memory mapping
For color text and CGA graphics modes, video memory is mapped to 16KB of addresses beginning at address B8000h, and in monochrome (MDA-compatible) text mode, video memory occupies 16KB beginning at B0000h. These address mappings are for backwards compatibility.
For modes new to the EGA, the video memory begins at address A0000h and occupies 64KB. The different base addresses for color vs. monochrome modes makes it possible for an EGA to be used simultaneously with a monochrome graphics card in the same computer, or for an EGA in MDA text mode to be used simultaneously with a CGA in the same computer.
EGA's native graphics modes are planar, as opposed to the interleaved CGA and Hercules modes. Video memory is divided into four "planes" (except 640 × 350×2, which has two planes), one for each component of the RGBI color space. Each pixel is represented by one bit in each plane. If a bit in the red plane is on, but none of the equivalent bits in the other pages are, a red pixel will appear in that location on screen. If all the other bits for that particular pixel were also on, it would become white, and so forth.
Planes are different sizes depending on the mode:
EGA video plane sizes
Mode
Plane size
200-line modes, 640 × 350×2 mode
8 KB
640 × 350 with 64 KB RAM
16 KB
640 × 350 with 128 KB RAM
32 KB
All planes reside at segment A000 in the CPU's address space. They are bank-switched, and only one plane can be read on the CPU bus at once; however, the programmer may set the control registers on the card to select which planes are written to and write to several at once. An exception is read mode1, in which all four planes are read and compared with programmed "Color Compare" data, and a byte indicating the result of comparing all four planes can be read on the I/O bus.
IBM 8514 is a graphics card manufactured by IBM and introduced with the IBM PS/2 line of personal computers in 1987. It supports a display resolution of 1024 × 768 pixels with 256 colors at 43.5 Hz (interlaced), or 640 × 480 at 60 Hz (non-interlaced). 8514 usually refers to the display controller hardware. However, IBM sold the companion CRT monitor which carries the same designation, 8514.
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, which became ubiquitous in the IBM PC compatible industry within three years. The term can now refer to the computer display standard, the 15-pin D-subminiature VGA connector, or the 640 × 480 resolution characteristic of the VGA hardware.
The Hercules Graphics Card (HGC) is a computer graphics controller formerly made by Hercules Computer Technology, Inc. that combines IBM's text-only MDA display standard with a bitmapped graphics mode, also offering a parallel printer port. This allows the HGC to offer both high-quality text and graphics from a single card.
The Personal System/2 or PS/2 is IBM's second generation of personal computers. Released in 1987, it officially replaced the IBM PC, XT, AT, and PC Convertible in IBM's lineup. Many of the PS/2's innovations, such as the 16550 UART, 1440 KB 3.5-inch floppy disk format, 72-pin SIMMs, the PS/2 port, and the VGA video standard, went on to become standards in the broader PC market.
The Color Graphics Adapter (CGA), originally also called the Color/Graphics Adapter or IBM Color/Graphics Monitor Adapter, introduced in 1981, was IBM's first color graphics card for the IBM PC and established a de facto computer display standard.
The Multi-Color Graphics Array or MCGA is a video subsystem built into the motherboard of the IBM PS/2 Model 30, introduced on September 2, 1986, and Model 25, introduced later on August 11, 1987; no standalone MCGA cards were ever made.
The Monochrome Display Adapter is IBM's standard video display card and computer display standard for the IBM PC introduced in 1981. The MDA does not have any pixel-addressable graphics modes, only a single monochrome text mode which can display 80 columns by 25 lines of high-resolution text characters or symbols useful for drawing forms.
Professional Graphics Controller is a graphics card manufactured by IBM for PCs. It consists of three interconnected PCBs, and contains its own processor and memory. The PGC was, at the time of its release, the most advanced graphics card for the IBM XT and aimed for tasks such as CAD.
The Plantronics Colorplus is a graphics card for IBM PC computers, first sold in 1982. It implements a superset of the then-current CGA standard, using the same monitor standard and providing the same pixel resolutions. It was produced by Frederick Electronics, a subsidiary of Plantronics since 1968, and sold by Plantronics' Enhanced Graphics Products division.
In computing, indexed color is a technique to manage digital images' colors in a limited fashion, in order to save computer memory and file storage, while speeding up display refresh and file transfers. It is a form of vector quantization compression.
The Olivetti M24 is a computer that was sold by Olivetti in 1983 using the Intel 8086 CPU.
The eXtended Graphics Array is a graphics card manufactured by IBM and introduced for the IBM PS/2 line of personal computers in 1990 as a successor to the 8514/A. It supports, among other modes, a display resolution of 1024 × 768 pixels with 256 colors at 43.5 Hz (interlaced), or 640 × 480 at 60 Hz (non-interlaced) with up to 65,356 colors. The XGA-2 added an 800 × 600 65,356 color mode and 1024 × 768 60 Hz non-interlaced.
VGA text mode was introduced in 1987 by IBM as part of the VGA standard for its IBM PS/2 computers. Its use on IBM PC compatibles was widespread through the 1990s and persists today for some applications on modern computers. The main features of VGA text mode are colored characters and their background, blinking, various shapes of the cursor, and loadable fonts. The Linux console traditionally uses hardware VGA text modes, and the Win32 console environment has an ability to switch the screen to text mode for some text window sizes.
The ATI Wonder is a series of video cards for the IBM Personal Computer and compatibles, introduced by ATI Technologies in the mid to late 1980s. These cards were unique at the time as they offered the end user a considerable amount of value by combining support for multiple graphics standards into a single card. The VGA Wonder series added additional value with the inclusion of a bus mouse port, which normally required the installation of a dedicated Microsoft Mouse adapter.
Tandy Graphics Adapter is a computer display standard for the Tandy 1000 series of IBM PC compatibles, which has compatibility with the video subsystem of the IBM PCjr but became a standard in its own right.
Composite artifact colors is a designation commonly used to address several graphic modes of some 1970s and 1980s home computers. With some machines, when connected to an NTSC TV or monitor over composite video outputs, the video signal encoding allowed for extra colors to be displayed, by manipulating the pixel position on screen, not being limited by each machine's hardware color palette.
The Quadram Quadcolor is a graphics card for IBM PC computers by Quadram Corporation, first sold in 1983. It is a superset of the then-current CGA standard, using the same monitor standard and providing the same pixel resolutions.
↑ Bermant, Charles (February 11, 1986). "EGA Standard Evolves for PC Graphics Users". PC Magazine. Ziff-Davis. 5 (3): 33–34. Archived from the original on February 20, 2024. Retrieved February 20, 2024– via Google Books.
↑ IBM Options and Adapters, Volume 1, "Enhanced Color Display", page 4: "When operating in Mode 1, the display maps the 4 input bits into 16 of the possible 64 colors as shown in the following chart." August 2, 1984.
This page is based on this Wikipedia article Text is available under the CC BY-SA 4.0 license; additional terms may apply. Images, videos and audio are available under their respective licenses.
