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Extended Graphics Array

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 65,536 colors. The XGA-2 added an 800 × 600 65,536 color mode and 1024 × 768 60 Hz non-interlaced.

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/ARegister-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==
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==
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==
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