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From: jca@pnet01.cts.com (John C. Archambeau)
Newsgroups: comp.sys.ibm.pc
Subject: Re: UNIX runs DOS applications?
Message-ID: <731@crash.cts.com>
Date: 19 Nov 89 00:16:05 GMT
Article-I.D.: crash.731
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mitsolid@acf5.NYU.EDU (Thanasis Mitsolides) writes:
>Thanks to everybody that responded.
>It is clear that When one moves to unix can take his DOS applications
>along. On a 386 machine at least which is what interests me anyway.
>
>Another question is:
>
>	Is it also possible for these DOS virtual machines to use
>	virtual memory? (ie in 4Mb of RAM a DOS Process uses expanded
>	memory of 40Mb (under a compatibility window in unix))
>
>	Is that asking for too much? :-)

My understanding of how DOS jobs work under a 386 and *nix based OS'es is 
this.  Each virtual DOS machine has it's own 8086 address space.  1 Mb of base
and if LIM EMS 4.0 is supported (and I know it is under SunOS 4.0.x and the
Sun 386i) that can be used.  As for how *nix handles that, it's just swapped
in and out as needed.  You can only put up to 16 Mb of main physical memory in
a Sun 386i, but it supports up to 4 Gb of virtual, so it swaps in and out the
rest if I recall correctly.  You can NOT however, say I want to give 4 Mb of
base to the DOS job and blah blah.  The term virtual 8086 machine is taken
literally, you literally have the 386 and VP/ix (aka DOS-Merge) juggling
multiple 8086 machines.  So I think the answer to your question is no, you
can't give 4 Mb of base memory to a DOS job.  But you can have the standard 1
1 Mb 8086 machine (note that only 640K of it is utilitized because of the
MS-DOS address space) and give it up to 32 Mb of LIM EMS 4.0 memory if your
*nix based OS and VP/ix (DOS-Merge) will support LIM.  I know the Sun 386i and
SunOS will.  My experience with 386 machines and *nix based OS'es revolves
around that.  SCO Xenix and Unix System V might do it differently, but I
doubt it.  Now 4 Mb of physical memory might be allocated to a virtual 8086
machine at some point and time since there might be LIM EMS 4.0 memory
involved.  If you're running a DOS job that runs DesqView, this is very
possible.  But you can not alter the physical address space of the 8086
machine.

This is an article in Sun Technology on how DOS Windows and the Sun 386i
works.  If you want a summary of it, I'll dig for it in the bookshelves at
work and post it.  I don't think that SCO's 386 products do it too
differently, and this also helps (in my opinion) to bring about an
understanding of how the 386 juggles virtual DOS machines.  If you just want
the issue, leave me e-mail and I'll tell you which one.

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