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From: mark@roissy.umd.edu (Mark Sienkiewicz)
Newsgroups: comp.os.386bsd.questions
Subject: Re: DOS/Windows under 386bsd (is there such?)
Date: 26 May 1993 13:40:08 GMT
Organization: University of Maryland
Lines: 22
Message-ID: <1tvrvo$eqa@umd5.umd.edu>
References: <1993May20.234750.5815@fcom.cc.utah.edu> <1993May21.135304.21185@cm.cf.ac.uk> <BLYMN.93May26170510@siren.awadi.com.au>
NNTP-Posting-Host: roissy.umd.edu
In article <BLYMN.93May26170510@siren.awadi.com.au> blymn@awadi.com.au (Brett Lymn) writes:
>
>Because of the way DOS-under-unix is implemented the only way you can
>run windows is in "real" mode (I think this is the right term...I
>really do hate these silly intel chips), that is, as if you were
>running things on an 8086. In fact this is what you are doing, by
>exploiting the virtual 8086 mode of the [34]86 chips you can run DOS
>as a unix process (with some supporting jiggery-pokery).
The name "real mode" refers to the fact that the memory references are to
_real_ addresses, not virtual addresses. It _is_ the term you are looking
for. I prefer to think of it as "bogus mode" because of the segment*16
+offset thing. :)
You can run virtual 8086 mode, but it doesn't do some things that 286's
do. If I understand the specs properly, it would be possible to implement
a 286 or 386 virtual machine (sort of like VM/370 does on the big IBM's) but
you would have to write code to handle all the MMU stuff, like loading
segment descriptors.
On the other hand... simulating EMS ("expanded memory") should be quite easy.