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From: mshute@r4.uucp (Malcolm Shute)
Newsgroups: comp.arch
Subject: Re: 64-bit addresses
Message-ID: <986@m1.cs.man.ac.uk>
Date: 21 Feb 90 12:22:22 GMT
References: <9708@spool.cs.wisc.edu> <20270@cfctech.cfc.com> <36080@mips.mips.COM> <168@csinc.UUCP>
Sender: news@cs.man.ac.uk
Reply-To: mshute@r4.UUCP (Malcolm Shute)
Organization: University of Manchester, UK
Lines: 34

>In article <36080@mips.mips.COM>, mash@mips.COM (John Mashey) writes:
>> Barry has a good analysis, but I'd observe a few other things:
and proceeds to observe that most people who think they want 64bit
addressing haven't thought through their reasoning, and realised that
they *could* live without it if they redesigned their proposed solution
properly.  But isn't this the point in current computer usage: hardware
is cheap, salaries are expensive.  If there is a 'natural' sledgehammer
approach which will ensure that the job is finished quickly, and
correctly (this follows from it being a 'natural' approach wrt to the
human minds that designed it) then it beats the more thought-intensive
solutions.

However, to change sides now, and argue the other way,
In article <168@csinc.UUCP> rpeglar@csinc.UUCP (Rob Peglar) writes:
>Today, I'm sure codes could use two-digit GB D-spaces (10-99 GB per
>file) if they had it.  [...]

I agree with this completely, as suggested by my paragraph above,
but this is just the first hurdle.  Assuming that it is accepted now
that applications *do* exist which *can* use such amounts of address
space; we now have the problem of establishing that the laws of
physics will *allow* them to use it.  "Barry's Good Analysis",
alluded to above, is a convincing one: how can we expect to see
machines with 64bit adrspc until we have machines that can do useful
things with it in small finite time?

The answer to the original poster's original question must surely
still be: "Not until instruction speeds are of the order of 4.0e9
times faster than they are at present (i.e. to cover 2^64 locations
in about the time that current processors take to cover 2^32 locations)",
or "Not until we can get 4.0e9 times as many processors sharing the
job of massaging all of those locations".

Malcolm Shute.         (The AM Mollusc:   v_@_ )        Disclaimer: all