Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!uwm.edu!zaphod.mps.ohio-state.edu!wuarchive!texbell!attctc!jolnet!cox
From: cox@jolnet.ORPK.IL.US (Ben Cox)
Newsgroups: comp.sys.ibm.pc
Subject: Re: MSDOS's recognition (?) of screen modes
Message-ID: <2593@jolnet.ORPK.IL.US>
Date: 29 Dec 89 06:10:36 GMT
References: <4703@itivax.iti.org>
Reply-To: cox@jolnet.UUCP (Ben Cox)
Organization: Jolnet, Public Access Unix, Orland Park (Joliet), Ill.
Lines: 27

In article <4703@itivax.iti.org> dhw@itivax.iti.org (David H. West) writes:
[deleted]
>The part I don't understand is as follows: I invoke the utility to
>set the card into, say, EGA graphics mode - I think the mode number
>is 16, but the manual is at home.  I then get a DOS prompt in a
>different text font.  What is happening here - is command.com
>temporarily returning the screen to (some other) text mode?  Or is
>the card clever enough to know it needs to simulate text even though
>it's "really" in a graphics mode?  Or does the card vendor's utility 
>not actually set a specific graphics mode, but rather enable a
>particular kind of emulation (even though I'm passing it a "mode 
>number", specifying number of pixels and colors, as a parameter)?
>And how does this square with the fact that if I set a "wrong"
>graphics mode, I don't even get a DOS prompt afterwards?

The BIOS knows how to put text on the screen, even in a bitmapped mode, and
COMMAND.COM calls the BIOS to put characters on the screen.  If the resolution
in the graphics mode is different from the resolution in the text mode, the
characters will look different.  If the BIOS doesn't know how to use a given
mode, you will not see characters, and you may hang (although sometimes you
can still type commands -- try typing "mode co80" sometime when you appear
hung -- it may be just that you don't see anything, even though you are not
hung -- you will reset to mode 3, which is 80x25 color text, or 7, which is
BW 80x25).

Ben Cox
b-cox2@uiuc.edu (gets forwarded to me wherever I am)