Path: utzoo!mnetor!uunet!seismo!sundc!pitstop!sun!decwrl!spar!freeman
From: freeman@spar.SPAR.SLB.COM (Jay Freeman)
Newsgroups: comp.arch
Subject: Re: More than 32 bits needed where?
Message-ID: <617@spar.SPAR.SLB.COM>
Date: 3 Feb 88 21:21:25 GMT
References: <235@unicom.UUCP> <28200089@ccvaxa> <3104@watcgl.waterloo.edu> <4340@ames.arpa>
Reply-To: freeman@spar.UUCP (Jay Freeman)
Organization: SPAR - Schlumberger Palo Alto Research
Lines: 37


The limits of a 32-bit address-space may not necessarily show up at the
high-price end of the market first:

To begin with, if I am not mistaken, the Saxpy Matrix -- a rather low-price
supercomputer -- can be ordered with up to 512 MByte of physical memory; I
believe Saxpy uses dynamic RAM in its system, and I think they are still
using 41256s.  If so, then an upgrade of this machine to a fully-populated
32-bit address space would appear feasible in the not too distant future,
when 4-MBit DRAMs become available.

Another argument:  At the site where I work there are several people who run
single tasks on Symbolics 3600 Lisp machines, that eat up several hundred
megabytes of address space.  The machines don't have nearly that much
physical memory, of course; most of the space used is swapped out to disc.
Notwithstanding, these users (a) are using almost 10 percent of the number
of bytes that a 32-bit byte-addressed machine can address; (b) are
continually asking for more swapping space (please, can't we buy some more
500-Meg discs?); and (c) have been doing so for at least three years.  On
this basis alone, I would say that the days of a 32-bit address space are
numbered.  Symbolics machines are on the pricey end of Lisp systems, but it
is only happenstance that these users are running on Symbolics hardware and
not on Suns.  For that matter, a lot of the newer micros are fast enough to
run decent Lisps; I can imagine needing the same several hundred megabytes
of swapping space for a Lisp system running on (say) a 386 box with Unix, or
on a Macintosh II with A/UX.

It kind of makes me wonder about many of the whizzy new processors; why
would anyone go to all the trouble to design and implement a new machine
with only a 32-bit bus?  If the new machines are as fast as reputed, then
probably Lisp users will want to run larger tasks than they can address.
What shall I do when my Sun-4 (or whatever) has 4 gigabytes of swapping
space and it's not enough?

						-- Jay Freeman

(canonical disclaimer: the opinions expressed are personal)