"When writing a 3D/2D engine do you need to be able to output to a output device such as a monitor? YES. Should you be able to display the output at different resolutions? YES. There you have it-> even DirectX's Direct3D uses DirectDraw to display output on the screen. The VESA organization set a few ground rules on accessing the Video memory in both a linear and page-type fashion.
Why is most of the pages only 64K in size? Years ago when IBM first developed the PC , they used 64K sizes because the 16-bit processors could only access 64K at a given time. Everything was split into 64K and when Hercules released the Hercules, it had 128K of ram - so it was split up in 64K pages. IBM thought it was a good idea to do the same to their EGA display card. The VGA followed and then SVGA because nobody wanted their graphic card to be incompatible with the standards"
FULL STORY @ COREMELTDOWN (http://www.coremeltdown.com/articles/3dprogramming/4.shtml)