| Extended Graphics Array (XGA) | |
| Predecessor: | 8514/A |
| Successor: | XGA-2 |
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 515K VRAM and additional $350 for the 512KB memory expansion (equivalent to $ and $, respectively, in).[1] 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.[2]
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.
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.
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.
The XGA offered:
XGA-2 introduced:
Later clone boards offered additional resolutions:
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.