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From: eric@cs.fau.edu (Eric Thav)
Newsgroups: comp.sys.ibm.pc.misc
Subject: Re: What's so special about the UMB?
Message-ID: <1991Jun06.030024.1439@cs.fau.edu>
Date: 6 Jun 91 03:00:24 GMT
References: <1991May30.213856.1@freke.claremont.edu>
Organization: Florida Atlantic University, Boca Raton
Lines: 24

In article <1991May30.213856.1@freke.claremont.edu> dhosek@freke.claremont.edu (Don Hosek) writes:
>What is it about the first 64K of extended mem that makes it so
>special to DOS 5.0, DESQview, et alia? It seems that there should
>be no more trouble accessing any other 64K block of extended mem
>than the UMB, but I'm acknowledgedly ignorant of such things...

From what I understand, they don't access it as extended memory.  Rather,
with HIMEM.SYS (or QEMM's appropriate drivers), programs that know about this
area can access that 64K block as CONVENTIONAL MEMORY.  Microsoft, when 
Windows 2.0 was introduced, "discovered" this area suddenly and developed the
HIMEM.SYS driver to access it.  So, when you load programs into it, you are
not exactly loading it into extended memory (even though it is located in
extended memory), but I believe the programs are just specifying that it
be located in an additional area of conventional memory (that just happens
to reside in the first 64K of extended memory).

Understand?


-- 
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Eric L. Thav                Florida Atlantic University - Boca Raton, FL
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