You might see if you can find "A Programmers
Guide to PC &
PS/2 Systems" Richard Wilton ,published by M-S Press. Came out
in 1987 and received rave reviews in all the trade publications. It
has ass. routine listings to access BIOS for CGA thru VGA and a
wealth of other info on the varios Dos video systems.
Or Michael Abrash's Black Book. (He worked on the Doom series of games) He
has a wonderful look at detailed access to the frame buffer (although he
focusses somewhat on VGA)
--Chuck