Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!usc!zaphod.mps.ohio-state.edu!uakari.primate.wisc.edu!xanth!mcnc!rti!bcw
From: bcw@rti.UUCP (Bruce Wright)
Newsgroups: comp.sys.ibm.pc
Subject: Re: USING TWO GRAPHICS CARDS IN A COMPAQ 386/25
Summary: Multiple video cards
Keywords: VGA CGA COMPAQ 386 GRAPHICS
Message-ID: <3369@rti.UUCP>
Date: 27 Dec 89 22:58:21 GMT
References: <5209@arctic.nprdc.arpa>
Organization: Research Triangle Institute, RTP, NC
Lines: 37

In article <5209@arctic.nprdc.arpa>, trejo@nprdc.arpa (Leonard J. Trejo) writes:
> We're trying to use two graphics cards in a Compaq 386/25 computer
> running MS-DOS 3.1.  One card is the Compaq Video Graphics Controller
> (VGA-compatible) and the other is the Compaq Video Display Controller
> (CGA-compatible).  We'd like to use, simultaneously, the VGA for 
> graphics-only display purposes only and the CGA as a text-only 
> console which echoes keyboard input.  Problem is that despite our 
> best efforts, graphics always go to the CGA card.  I'm told that 
> this is because VGA and CGA screen memory overlap, plus that 
> whenever another graphics card is installed with the Compaq VGA, 
> graphics are forced to go to the other card and the VGA runs in 
> monochrome mode.

You can install an MDA or a Hercules card, as some have noted, at 
least with a few VGA boards (this is more commonly done with EGA, 
I'm not sure it's "officially" supported for VGA).

There are also a few companies that sell video cards that can be
configured to allow multiple EGA or multiple VGA cards in the same
machine at the same time (I've seen it done, but don't remember the
company names offhand).  The cards work by a variation on a bank-
switching scheme:  an extra, nonstandard register exists which tells
the graphics cards which one is to be the currently active card.  This
allows the vast majority of standard PC software to be run on the cards
without modifications.

You probably can't do anything like that with the Compaq cards unless
you can figure out a way to retrofit such a scheme onto the cards, and
this is unlikely and would require significant hardware expertise.

Be warned that the cards I've heard about that allow this sort of
thing are *expensive* - I seem to remember that they retailed for around
$1000.  Lots cheaper than a second PC though, if you are running them in
a fast 386 with lots of disk space.  The computer I saw them on was a
Compaq 386, BTW ...

						Bruce C. Wright