Path: utzoo!ncc!alberta!calgary!radford
From: radford@calgary.UUCP (Radford Neal)
Newsgroups: comp.arch
Subject: Re: More than 32 bits needed where?
Summary: Why does 64 come after 32?
Keywords: integer range, 32 bits, 64 bits
Message-ID: <1333@vaxb.calgary.UUCP>
Date: 4 Feb 88 18:40:13 GMT
References: <235@unicom.UUCP> <28200089@ccvaxa> <3104@watcgl.waterloo.edu> <4340@ames.arpa>
Organization: U. of Calgary, Calgary, Ab.
Lines: 29

In article <4340@ames.arpa>, lamaster@ames.arpa (Hugh LaMaster) writes:

> I also note that large multi-CPU mainframes (e.g. IBM, NAS, Amdahl,...) as
> well as supercomputers are approaching the 32 bit addressing limit for
> PHYSICAL memory.  So, I predict a healthy future for 64 bit machines in
> the "data processing" world, as well as in the scientific computing world.
> It might even be coming sooner than some people think in the micro-computing
> world.

Why is everyone assuming that if you want greater than 32 address bits
you need 64? My guess is that 48 (or maybe even 40) bit addresses will
be used. If you assume that memory is dominated by such addresses, or
other quantities held in the same word size, going to 64 costs 33% more
than using 48. Note that for the systems mentioned, memory must surely 
be a large part of the total cost.

Now I can see the flames coming on this one... How increadibly short
sighted! History shows that we *always* need more address bits... Please
calculate the amount of memory addressable with 48 bits, then ask whether
systems with this much memory, if they ever appear, will have anything
like a current machine architecture anyway...

Of course, there are other reasons for wanting long addresses, than just
access to physical memory. If you want sparse address spaces, typed
pointers, ring brackets, whatever, more power to you (MULTICS already
has *72* bit pointers...)

    Radford Neal
    The University of Calgary