Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!uwm.edu!csd4.csd.uwm.edu!markh
From: markh@csd4.csd.uwm.edu (Mark William Hopkins)
Newsgroups: comp.os.msdos.programmer
Subject: Re: accessing video RAM: how advisable is it?
Message-ID: <10584@uwm.edu>
Date: 28 Mar 91 23:24:34 GMT
References: <9103162053.AA02053@samadams.Princeton.EDU>
Sender: news@uwm.edu
Organization: University of Wisconsin - Milwaukee
Lines: 18

In article <9103162053.AA02053@samadams.Princeton.EDU> tr@SAMADAMS.PRINCETON.EDU (Tom Reingold) writes:
>Are PC's running DOS more compatible with IBM video cards these days
>than they were when MS-DOS came out?

BIOS video modes 0 to 10 in IBM compatibles have buffers at segment address
b800, except video mode 7 whose segment address is at b000.  Video modes 13 to
19 are a000.

Video memory to screen mapping is different for different modes though.

There is a BIOS function that allows you to determine the current PC model
you're running on, to determine the current video mode and I think to determine
whether such and such a video mode can be set up in the current hardware.

The book "IBM Microcomputers A programmer's handbook" by Julio Sanchez
and Maria Canton describes absolutely everything a programmer needs to know
about this and almost all other parts of the IBM and BIOS.  BIOS interrupt
10 (hex) contains all the video service routines.