Path: utzoo!news-server.csri.toronto.edu!cs.utexas.edu!swrinde!elroy.jpl.nasa.gov!ncar!csn!kessner!david
From: david@kessner.denver.co.us (David Kessner)
Newsgroups: comp.os.msdos.programmer
Subject: Re: accessing video RAM: how advisable is it?
Message-ID: <1991Mar16.222835.2045@kessner.denver.co.us>
Date: 16 Mar 91 22:28:35 GMT
References: <9103162053.AA02053@samadams.Princeton.EDU>
Reply-To: david@kessner.denver.co.us (David D. Kessner)
Organization: Kessner, Inc
Lines: 32

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?  Years ago, you were asking for
>trouble if you wrote directly to video RAM because many cards had their
>display buffers at various addresses.  Is this no longer true?  I'd
>like to know because it would be nice if the product I am developing
>didn't need to care.
>
>Also, are the two addresses still the only ones to worry about?  There
>is one for monochrome and one for color, including CGA, EGA and VGA.
>--
>        Tom Reingold
>        tr@samadams.princeton.edu  OR  ...!princeton!samadams!tr

These days it is expected that you will write directly to video RAM.  It is
considered a fact of life.  You might have compatability problems with some
really strange computers (like those not-quite compatables from 1983 or so), 
but I wouldent worry about these-- no-one else does!

Yes, there are only two addresses of TEXT VIDEO RAM to worry about.

I have written a program that is currently in use on over 100 machines-- from
the original PC to 386's.  It figures out which address to use, then writes
directly to it.  Out of those 100+ machines, I have never ran into 
compatability problems (even on a few Tandys :).  

Hope that helps...

-- 
David Kessner - david@kessner.denver.co.us            | do {
1135 Fairfax, Denver CO  80220  (303) 377-1801 (p.m.) |    . . .
If you cant flame MS-DOS, who can you flame?          |    } while( jones);