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From: mh2f+@andrew.cmu.edu (Mark Hahn)
Newsgroups: comp.arch
Subject: Re: 64 bit addresses
Message-ID: <obimZ2a00VotQ3v2oF@andrew.cmu.edu>
Date: 15 Feb 91 00:20:18 GMT
References: <cbiAekK00VpINR8nEq@andrew.cmu.edu>,
	<1991Feb13.212041.14368@news.arc.nasa.gov>
Organization: Carnegie Mellon, Pittsburgh, PA
Lines: 30
In-Reply-To: <1991Feb13.212041.14368@news.arc.nasa.gov>

as I think about it more, 64 bits is a really bad idea.
for people like Hugh LaMaster, it's great, because everyone
seems to be seeing it his way: that 64 bits as inevitable
because 32bits as already obsolete.  note that very few
people deal with large arrays as I have to assume he does.

is it true that 32bits is obsolete?  certainly not on workstations, 
where I'd guess the median is only about 24bits of physical memory,
with maybe 29bits of hard disk.  remember that current CPUs 
only have a throughput of about 24bits, no matter whether you like 
FLOPS or MIPS or strcmp's or pointer dereferences.  I suppose
patient people will disagree...

still, my original post on this subject was attempting to find 
a 64bit rationale for the rest of us, who have more diverse
activities like using skiplists or SML or editors whose internals
are lisp or which represent text as a list of chunks.
where does 64bits make sense?  in a relatively small market:
databases, fileservers, numeric analysis and simulation.
in other words 64bit addresses aren't worth the cost to most users,
even ignoring the the unwashed masses using PCs with ~20bits.

so this leads to the question: is MIPS crazy?  It depends on
whether they can make the BigData people happy while not losing
their major market.  perhaps this is the first sign that they
want to split to serve two product lines.  they obviously have to
watch their step to remain competitive in the 32bit market, 
with SPARC and Moto already seeming to pull ahead.

regards, mark