Extended Graphics Array
Introduction 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 65,356 colors. The XGA-2 added an  65,356 color mode and  60 Hz non-interlaced.The XGA was introduced at $1095 with 515K 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, $, respectively, in ).
Features IBM micro channel architecture XGA graphics card 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 8514 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===IBM micro channel architecture XGA-2 graphics card XGA-2 added support for non-interlaced  and made 1MB VRAM standard. It had a programmable PLL circuit and pixel clocks up to 90MHz, 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 with 256 colors out of 262,144 (18 bit RGB); text mode with 80×34 characters;*'''''' graphics with 256 colors out of 262,144 (18-bit); text mode with 85×38 or 146×51 characters;*'''''' with 16-bit "high color"XGA-2 introduced:*'''''' graphics with 256 colors out of 16.7M (24-bit);*'''''' graphics with 256 colors out of 16.7M (24-bit);*'''''' with 16-bitLater clone boards offered additional resolutions:*'''''' with 24-bit color depths;*'''''' with 24-bit color depths;*'''''' with 16-bit and 24-bit color depths
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 **