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From: rjn@duke.UUCP (R. James Nusbaum)
Newsgroups: net.arch
Subject: Re: Reasons For Large Main Memories
Message-ID: <8511@duke.duke.UUCP>
Date: Thu, 4-Sep-86 11:11:40 EDT
Article-I.D.: duke.8511
Posted: Thu Sep  4 11:11:40 1986
Date-Received: Fri, 5-Sep-86 19:45:09 EDT
References: <8494@duke.duke.UUCP> <147@eneevax.UUCP>
Reply-To: rjn@duke.UUCP (R. James Nusbaum)
Distribution: na
Organization: Duke University, Durham NC
Lines: 35

In article <147@eneevax.UUCP> hsu@eneevax.UUCP (Dave Hsu) writes:
>
>All good and well, Jim, but not the topic of discussion.  By `large' we
>mean on the order of Gbytes, not Mbytes, at which point various other
>factors in the system design can degrade performance substantially.
>With a database of hundreds of Gbytes, the paging problems facing a
>hypothetical programmer with one or two Gbytes of RAM can actually be much
>worse than those facing a programmer with one or two Mbytes worth.
>All it takes is a few zillion page faults, and the time lost in page-
>search-and-replacement can easily exceed the time gained by a slightly
>reduced number of accesses.
>
>babbling again,
>
>-dave
>-- 
>David Hsu  (301) 454-1433 || -8798 || -8715	"I know no-thing!" -eneevax

Your point is also true.  However many Lisp systems are single user systems.
Having even a couple of hundred megawords of memory could totally eliminate
paging, as the entire system could be resident.  Take the Symbolics for
instance.  It has a 200Mb disk used for paging and some middle amount of 
memory (maybe 16Mb).  We have run many complex systems in this 200Mb size.
If we had 200Mb of memory then we would have no need for paging at all!  This
would significantly speed up many applications.

Even 200Mb won't be enough in the near future for some applications, mainly
the VLSI cad systems I've worked on.  And considering the large word size
of some Lisp machine designs (in order to have tag bits) 200Mb can work out
to be only 40Mw.  My whole point, which I admit I didn't get across well, was
that some systems could totally eliminate paging by having huge amounts of
actual memory.  These systems would generally be single user systems, like
Lisp, APL and possibly Prolog machines.

Jim Nusbaum