Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!wuarchive!gem.mps.ohio-state.edu!apple!oliveb!tymix!cirrusl!sunscreen!glen
From: glen@sunscreen.UUCP (Glen Ivey)
Newsgroups: comp.sys.ibm.pc
Subject: Re:  What's Extented memory good for??
Summary: Not much
Keywords: extended memory help
Message-ID: <865@cirrusl.UUCP>
Date: 19 Sep 89 18:12:29 GMT
Sender: news@cirrusl.UUCP
Organization: CIRRUS LOGIC Inc.
Lines: 44


    Ok, a few definitions:

Extended Memory == Memory at addresses above 1Mb.  This was introduced
w/ the advent of the PC-AT and the '286, because the '86/'88
processors only had 20 address bits.  (2 ** 20 = 1M)

Expanded Memory == Memory that lies bellow 1Mb, and is accessed by
bank switching using the LIM protocol.  (If there is something called
"expanded" that does not use LIM, I'd be interested in hearing about
it.)

    Now, many add-in memory cards have configuration options that
allow extended or expanded addressing.  If you're extra Mb is
implemented like this, you may be able to get around your problem.

    The other catch is that there is no way to convince vanilla DOS
software that the extra memory exists.  Extended memory, because it
relies on the "Virtual Protected Mode" addressing provided by the '286
(and follow ons), can not be used by DOS programs unless they contain
the software to constantly change the processor mode.  Many RAM disk
drivers, and a few applications use this method.  Expanded memory also
requires software that knows about the memory configuration.  Because
LIM is a bank switched system, only a small portion of the total
expanded memory is available at any one time, and the memory
management in the application must be designed to accommodate this.

>                         What I really want to do is use that EXTENDED
>memory as CONVENTIONAL memory.

    Your problem basically comes down to the fact that "conventional"
memory (by which, I assume you mean memory accessible to a program
that doesn't make a special effort to accommodate expanded/extended
memory) is limited by the original MS-DOS/8086 architecture, and,
short of moving to OS/2 (which has a software memory management
architecture based on the '286 virtual protected mode) and replacing
your software, there's nothing to do about it.

===============================================================================
Glen Ivey        {ames,uunet,amdahl}!oliveb!cirrusl!glen
Cirrus Logic     glen%cirrusl%oliveb@ames.arc.nasa.gov
--Not only are my opinions not necessarily my companies, they aren't
always mine either.
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