Extended Graphics Array

The eXtended Graphics Array (usually called XGA) 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 pixels with 256 colors at 43.5  Hz (interlaced), or at 60 Hz ( non-interlaced) with up to 65,536 colors. The XGA-2 added an 65,536 color mode and 60 Hz non-interlaced.

The XGA was introduced at $1095 with 512K VRAM and additional $350 for the 512KB memory expansion (equivalent to $ and $, respectively, in ). As with the 8514/A, XGA required a Micro Channel architecture bus at a time when ISA systems were standard, however due to more extensive documentation and licensing ISA clones of XGA were made. XGA was integrated into the motherboard of the PS/2 Model 95 XP 486.

An improved version called XGA-2 was introduced in 1992 at $360, worth $ in dollars.

XGA gives its name to the resolution , as IBM's VGA gave its name to , despite the IBM 8514/A and PGC cards respectively supporting those resolutions prior to the eponyms.

Features

The 8514 had used a standardised API called the "Adapter Interface" or AI. This interface is also used by XGA, IBM Image Adapter/A, and clones of the 8514/A and XGA such as the ATI Technologies ''Mach 32'' and IIT ''AGX''. The interface allows computer software to offload common 2D-drawing operations ( line-draw, color-fill, and block copies via a blitter) onto the hardware. This frees the host CPU for other tasks, and greatly improves the speed of redrawing a graphics visual (such as a pie-chart or CAD-illustration). Hardware-level documentation of the XGA was also made, which had not been available for the 8514/A.

XGA introduced a 64x64 hardware sprite which was typically used for the mouse pointer.

Differences from 8514/A

*Register-compatible with VGA
*Adds a 132 column text mode and high color in
*Requires a minimum of 80386 host CPU
*Provides a 3-dimensional drawing space called a "bitmap" which may reside anywhere in system memory
*Adds a sprite for a hardware cursor
*The Adapter Interface driver is moved to a .SYS file instead of TSR program
*Provisions made for multitasking environment
*XGA can act as bus master and access system memory directly
*Hardware level documentation has been provided by IBM

XGA-2

XGA-2 added support for non-interlaced and made 1MB VRAM standard. It had a programmable PLL circuit and pixel clocks up to 90 MHz, enabling a 75 Hz refresh rate at . The resolution was added with 16 bit high color support. The DAC was increased to 8 bits per channel, and the accelerated functions were enabled at 16 bit color depth. Faster VRAM also improved performance.

Output capabilities

The XGA offered:
*:
**graphics mode with 256 colors at once (8-bit) out of 262,144 ( 18-bit RGB palette);
**graphics with 65,536 colors at once ( 16-bit "high color");
**text mode with 80×34 characters
*:
**graphics with 256 colors out of 262,144;
**text with 85×38 or 146×51 characters

XGA-2 introduced:
* graphics with 256 colors out of ''16.7M (24-bit palette)'';
*' graphics with 65,536 colors at once;
* graphics with 256 colors out of ''16.7M''

Later clone boards offered additional resolutions:
* graphics with ''16.7M'' accessible colors at once (if it were possible with pixels) ''(24-bit "true color")'';
* graphics with ''16.7M'' colors at once;
*' graphics with 65,536 and 16.7M colors at once

Clones

Unlike with the 8514/A, IBM fully documented the hardware interface to XGA. Further, IBM licensed the XGA design to SGS-Thomson (inmos) and Intel. The IIT AGX014 was largely compatible with the XGA-2 and offered some enhancements.

The VESA Group introduced a common standardized way to access features like hardware cursors, Bit Block transfers ( Bit Blt), off screen sprites, hardware panning, drawing and other functions with VBE/accelerator functions (VBE/AF) in August 1996. This, along with standardised device drivers for operating systems such as Microsoft Windows, eliminated the need for a hardware standard for graphics.

See also

*List of IBM products
* List of defunct graphics chips and card companies

References

Further reading

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{{IBM personal computers

Computer display standards
IBM video hardware
Graphics cards
Computer-related introductions in 1990
Computer-related introductions in 1992
IBM PS/2