Path: utzoo!utgpu!watserv1!watmath!att!occrsh!uokmax!apple!sun-barr!cs.utexas.edu!uunet!mcsun!ukc!harrier.ukc.ac.uk!zodiac.ukc.ac.uk!cur022
From: cur022@zodiac.ukc.ac.uk (Bob Eager)
Newsgroups: comp.os.misc
Subject: Re: Multics - Whats the current sta
Message-ID: <20907.26e6edac@zodiac.ukc.ac.uk>
Date: 7 Sep 90 00:45:32 GMT
References: <44101@<1990Aug30> <72900004@.Prime.COM>
Organization: Computing Lab, University of Kent at Canterbury, UK.
Lines: 23

In article <72900004@.Prime.COM>, EAF@.Prime.COM writes:
> Unfortunately the 386 and 486 do not feature a page table for every
> segment, even though they do have rings of protection.  Further if I understand
> correctly, they do not have protection at the segment level but rather
> at the page level.  These facts would make the "simulation" of multics
> difficult.

I worked on a MULTICS-style OS for some years, and idly looked at the 386
architecture to see if it could be done on there.

I think the thing to do is to ignore the 386 segments - just map a couple
of 4GB ones on to the whole VM (one for code, one for data). For the MULTICS
segments, use page directories - you get 1MB 'segments' (in MULTICS terms)
then.

The use of the term 'segment' for the Intel 8088-style contruct (albeit bigger
on the 386) tends to push one's thinking in the wrong direction...
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Bob Eager            | University of Kent at Canterbury
rde@ukc.ac.uk        | +44 227 764000 ext 7589
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