Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!bbn!usc!pollux.usc.edu!papa
From: papa@pollux.usc.edu (Marco Papa)
Newsgroups: comp.sys.amiga
Subject: Re: Multi-tasking and OS books
Message-ID: <17212@usc.edu>
Date: 14 May 89 06:54:28 GMT
References: <17148@usc.edu> <24279@agate.BERKELEY.EDU> <18268@cup.portal.com> <17183@usc.edu> <11336@polyslo.CalPoly.EDU> <17195@usc.edu> <11373@polyslo.CalPoly.EDU> <17207@usc.edu> <5863@cs.Buffalo.EDU>
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Reply-To: papa@pollux.usc.edu (Marco Papa)
Organization: Felsina Software, Los Angeles, CA
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In article <5863@cs.Buffalo.EDU> ugkamins@sunybcs.UUCP (John Kaminski) writes:
>You seem to confuse preemptive scheduling capability and hardware requirements
>for it.  Since when does an 8088 have a supervisor mode?
>(not intending to flame, but curious why you seem a bit self-contradictory)

You're quite right.  UNIX on the 8088 has mostly been implemented using a
timer interrupt. Supervisor mode, when available, helps preventing access
to kernel protected areas.  The main point stands: you need really a little
to implement a preemptive OS. (on the 80286 UNIX usually uses supervisor mode
inside the kernel). On the IBM PC Level 0, the highest interrupt priority,
is attached to Channel 0 of the timer/counter and therefore is the best
candidate to use for preemptive scheduling. Back to the Amiga .... :-)

-- Marco Papa 'Doc'
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