XGA Device Description

The I/O registers mostly are readable and writable, plus a few reserved registers.
It is a BusMaster device, capable of DMA operations.
DMA (co-processor) operations are initiated through memory-mapped I/O registers located in the adapter ROM area above C0000.
The device can operate in a virtual memory (that is, a 386 environment).
Video memory can be accessed by the DOS application through either an A0000 or B0000 aperture, without use of a co-processor.
Multiple XGA configuration is possible.
With built-in VGA hardware, the two operating environments are mutually exclusive even though they share the same DAC and VRAM.
Planar VGA is disabled on a single display system (the display is attached to the XGA adapter).
132-column text mode is supported.
All graphics modes are packed-pel.