Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!snorkelwacker!spdcc!esegue!johnl
From: johnl@esegue.segue.boston.ma.us (John R. Levine)
Newsgroups: comp.sys.ibm.pc
Subject: Re: processor wars.
Summary: You can't partition a 386.
Message-ID: <1990Jan4.232250.4359@esegue.segue.boston.ma.us>
Date: 4 Jan 90 23:22:50 GMT
References: <6767@tank.uchicago.edu> <1989Dec17.112127.27333@me.toronto.edu> <3368@rti.UUCP> <899@lzaz.ATT.COM> <1989Dec29.165724.12683@sj.ate.slb.com> <199@tw-rnd.SanDiego.NCR.COM> <1990Jan4.172835.2493@sj.ate.slb.com>
Reply-To: johnl@esegue.segue.boston.ma.us (John R. Levine)
Organization: Segue Software, Cambridge MA
Lines: 37

In article <1990Jan4.172835.2493@sj.ate.slb.com> poffen@sj.ate.slb.com (Russ Poffenberger) writes:
>In the 386 architecture, you can partition the memory to look like a number
>of independent '86 machines. It is called virtual '86 mode. By assigning
>a chunk of memory (640K) in this virtual mode, you can run MSDOS in it
>without it knowing that other operating systems are also running on the same
>machine.

Jeepers, get your facts straight.  The 386 lets you put any user mode process
into virtual 86 mode which makes that process execute 8086 instructions
rather than 386 instructions.  The DOS under Unix packages, VP/ix and DOS
Merge use that mode but depend on the Unix operating system to do disk and
terminal I/O.  The DOS process is a user mode process subject to the same
protection, preemption, and paging as any other Unix user process.

Virtual 86 mode is very handy for running all the useful software that
depends on DOS while really running Unix, but it critically depends on the
operating system that is in charge.  (We disregard here the DOS EMS managers
that use V86 mode solely to get access to the page mapping tables, they
hardly count.)  It is in no sense a partitioning scheme.

>>I really >don't think OS/2 and Unix would cooperate very well running at the
>>same time.
>Certainly a small amount of work might have to be done when it comes to
>sharing peripherals, but it could be done.

Virtual 86 mode gives you an 8086, not a 286, so you can't run OS/2 in a
process.  Furthermode, OS/2 and Unix both expect to control all of the memory
management, segmentation, I/O addresses, devices, and interrupts, and a huge
amount of surgery would be necessary to both to allow them to get out of
each other's way.  Don't hold your breath.  I expect that what you will see
is a Posix-compliant interface under OS/2-386, and OS/2 will evolve into yet
another flavor of Unix, shortly after V.4 heals the 15 year schism between
USG and Berkeley Unix.  Just what we need.
-- 
John R. Levine, Segue Software, POB 349, Cambridge MA 02238, +1 617 864 9650
johnl@esegue.segue.boston.ma.us, {ima|lotus|spdcc}!esegue!johnl
"Now, we are all jelly doughnuts."