Path: utzoo!attcan!uunet!husc6!bloom-beacon!mit-eddie!ll-xn!ames!killer!tness7!bellcore!faline!thumper!ulysses!gamma!pyuxp!pyuxe!pyuxf!asg
From: asg@pyuxf.UUCP (alan geller)
Newsgroups: comp.arch
Subject: Re: Is the Intel memory model safe from NO-ONE ?!?
Summary: Like VAX or Motorola PMMU??
Message-ID: <316@pyuxf.UUCP>
Date: 11 May 88 16:19:02 GMT
References: <1806@obiwan.mips.COM> <2904@omepd> <353@cf-cm.UUCP> <953@cresswell.quintus.UUCP>
Organization: Bell Communications Research
Lines: 60
Posted: Wed May 11 12:19:02 1988

In article <953@cresswell.quintus.UUCP>, ok@quintus.UUCP writes:
> ...
> "Segments" on the Burroughs machines are like "objects" in SmallTalk,
> and the original memory management scheme on those machines was not
> unlike object swapping.  There is no such thing as a virtual address
> as such, you can only talk about a location within an object.  Since
> segments usually correspond to logical entities (such as files,
> arrays, procedures, &c) this means that wild addressing out of an
> array is simply impossible.  On a Burroughs system, separate processes
> can share objects (arrays, open files, &c) without having to share
> intervals of their address space, worrying about page boundaries &c.
> 
> "Segments" in the 8086 are indeed a kludge to buy you 20-bit addressing
> on a 16-bit machine.  Just because two segment registers hold different
> values doesn't mean that you can't address the same location through them.
> 
> Segment registers on the 80386 can be used for either purpose, depending
> on the operating system, but there really aren't enough segment numbers
> to do much in the way of segments as objects, and system V/386 simply
> ignores them.
> 
> The problem isn't 16-bit or 32-bit or N-bit address spaces,
> it's the assumption that an address space is a one-dimensional array.
> Viva tree-structured address spaces!


You mean, like the memory model provided by heirarchical page translation
tables, such as the VAX or Motorola PMMU?

Alan Geller
Bellcore
...!{princeton,rutgers}!bellcore!pyuxp!pyuxf!asg

If I don't know what I'm saying, how can my employer?


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