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From: dmurdoch@watstat.waterloo.edu (Duncan Murdoch)
Newsgroups: alt.msdos.programmer,comp.sys.ibm.pc
Subject: Re: i/o routines and non-standard video modes
Message-ID: <966@maytag.waterloo.edu>
Date: 5 Dec 89 14:18:43 GMT
References: <2090@calvin.EE.CORNELL.EDU> <2980@einstein.ptolemy.arc.nasa.gov> <2092@calvin.EE.CORNELL.EDU> <2544@alva.tut.fi> <89320 <1494@cc.helsinki.fi> <89338.051609CMH117@PSUVM.BITNET>
Sender: daemon@maytag.waterloo.edu
Reply-To: dmurdoch@watstat.waterloo.edu (Duncan Murdoch)
Organization: U. of Waterloo, Ontario
Lines: 20

In article <89338.051609CMH117@PSUVM.BITNET> CMH117@PSUVM.BITNET (Charles Hannum) writes:
>>especially more.
>
>You are naive.  DOS only *thinks* it knows what size the screen is.  In
>reality, if you set the screen size without using MODE, DOS won't know a
>damned thing about it.  How about using "MODE ,50" and having a program set
>the screen back to 25 line mode.  What will DOS do?  Heh, heh ...

Any program that changed the screen size without updating the screen size
bytes in the BIOS data area (40:4A = number of columns, 40:4C = number
of bytes in the full screen) is buggy and should be thrown out.  If DOS
can't read those values and use them, then it's buggy and should be thrown
out.  (This is the recommended action for ANSI.SYS, by the way.  It contains
the hard coded screen length in earlier versions of DOS.  Plain DOS can
handle a 50 line screen with no trouble.) 

Duncan Murdoch

P.S. If there are any errors in the information above, then please
throw it out.