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From: ralf@B.GP.CS.CMU.EDU.UUCP
Newsgroups: comp.sys.ibm.pc
Subject: Re: Extended/Expanded Memory
Message-ID: <251@PT.CS.CMU.EDU>
Date: Wed, 28-Oct-87 12:27:47 EST
Article-I.D.: PT.251
Posted: Wed Oct 28 12:27:47 1987
Date-Received: Sat, 31-Oct-87 08:48:40 EST
References: <7405@dartvax.UUCP> <7662@steinmetz.steinmetz.UUCP> <221@PT.CS.CMU.EDU> <7700@steinmetz.steinmetz.UUCP>
Sender: netnews@PT.CS.CMU.EDU
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Organization: Carnegie-Mellon University, CS/RI
Lines: 42
Keywords: Going from one to the other

In article <7700@steinmetz.steinmetz.UUCP> davidsen@crdos1.UUCP (bill davidsen) writes:
>In article <221@PT.CS.CMU.EDU> I write:
>|In article <7662@steinmetz.steinmetz.UUCP> davidsen@crdos1.UUCP (bill davidsen) writes:
>|>QEMM from Quarterdeck seems to work quite well. I have the 386 version,
>|>but I'm told that there is a 286 version as well. It's absolutely possible.
>|>	bill davidsen		(wedu@ge-crd.arpa)
>|
>|The QEXT.SYS driver which comes with DV 2.0 calls itself QEXTXXX0, and has
>|the startup message "QUARTERDECK EXTENDED MEMORY MANAGER".  If this is
>|what you are thinking of, it will *not* allow you to use extended memory
>|as expanded memory.  What it DOES do is allow DESQview to run about 60K of
>|itself in the first 64K of extended memory *without* switching to protected
>|mode.
>
>I don't know exactly what it does. I can run 4 600k DOS programs at
>once, so I assume that it does what the manual say: allows extended
>memory to be used as expanded memory. [...]
>	bill davidsen		(wedu@ge-crd.arpa)


I guess I wasn't explicit enough:  I was talking about a driver which is
included in the base package, *not* the extra-cost QEMM-386.  The 386 version
does indeed simulate EEMS memory, but that is trivial on a 386 compared to
a 286 (386: run in virtual 86 mode, modify page tables; 286: do actual
physical copying, switching back and forth between real and protected mode).
And of course far faster.

Yes, there are EMS simulators for 286's, but as I mentioned above, they
work by actually copying data to and from a fixed 64K memory buffer.  It is
much harder to simulate AshtonTate-AST Enhanced EMS (EEMS) memory, because
that would require that the driver be able to swap any portion of the DOS
address space.  Note that DESQview requires EEMS (not EMS) to be able to
run more than 640K of programs concurrently without swapping some out.
Simulated EEMS, however, would bring DV to its knees--try task switching
three or four times a second when it takes a full second or more to swap
address spaces with an EEMS simulator.

-- 
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