Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!husc6!think!ames!ucsd!ucsdhub!hp-sdd!hplabs!sri-unix!quintus!ok
From: ok@quintus.UUCP (Richard A. O'Keefe)
Newsgroups: comp.arch
Subject: Re: Is the Intel memory model safe from NO-ONE ?!?
Message-ID: <977@cresswell.quintus.UUCP>
Date: 14 May 88 11:00:50 GMT
References: <1806@obiwan.mips.COM> <2904@omepd> <353@cf-cm.UUCP> <316@pyuxf.UUCP>
Organization: Quintus Computer Systems, Mountain View, CA
Lines: 26

In article <316@pyuxf.UUCP>, asg@pyuxf.UUCP (alan geller) writes:
> In article <953@cresswell.quintus.UUCP>, ok@quintus.UUCP writes:
> > 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?
> 
Each process on a VAX sees a LINEAR address space.  Page tables are part
of the implementation of that, and are not part of the applications
programmer's view of the architecture.  I don't know much about the
Motorola PMMU, but what I recall is that again it is implementation
kruft supporting a LINEAR address space.  People are complaining about
32-bit address spaces because they have their "an address space is an
array of storage units each of which is identified by a single integer"
blinkers on.  I explicitly said "viva tree-structured address spaces".
{Ok, I should *really* have said "graph-structured".}  The kind of thing
I have in mind is a system where the virtual memory space is pretty much
like the UNIX file system.  To get to a byte, you specify a sequence of
integers, like a Dewey number.  A very simple case would be that a
segment is either an array of bytes or an array of segments.  There might
be more than one path to a segment, or there might not.  On the B6700,
physical memory was limited to 6 Mbytes, but the only limit (in principle)
on the size of your virtual memory was the amount of disc you had for
paging.