Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!uunet!mcsun!ukc!edcastle!aiai!richard
From: richard@aiai.ed.ac.uk (Richard Tobin)
Newsgroups: comp.arch
Subject: Re: 64-bit addresses
Message-ID: <1833@skye.ed.ac.uk>
Date: 23 Feb 90 18:58:17 GMT
References: <36080@mips.mips.COM>
Reply-To: richard@aiai.UUCP (Richard Tobin)
Organization: AIAI, University of Edinburgh, Scotland
Lines: 26

In article <36080@mips.mips.COM> mash@mips.COM (John Mashey) writes:
>	a) What applications have you seen that wanted >32 bits of space?

Consider a language (prolog for example) that is implemented with
multiple stacks (maybe 2-4).  It's nice (a) not to have to check for
stack overflow and (b) to be able to expand the stacks without
relocating and fixing up all the pointers.  If you can spread your
stacks around virtual memory and unmap pages at the ends of the
stacks, you can do this.  In general, 4Gbytes of virtual address space
is plenty.

Now consider the same language with multiple threads, each requiring
(say) 2 stacks.  It's no longer clear that 4Gbytes is enough (though
it often will be - threads are often used for fairly simple tasks, 
with perhaps one really big one doing the hard work).

>	b) DId they need it, or justtake it because they had it?

Well, I haven't seen such a system on a machine with more than 32 bits
of address space, and people manage without.

-- Richard
-- 
Richard Tobin,                       JANET: R.Tobin@uk.ac.ed             
AI Applications Institute,           ARPA:  R.Tobin%uk.ac.ed@nsfnet-relay.ac.uk
Edinburgh University.                UUCP:  ...!ukc!ed.ac.uk!R.Tobin