Path: utzoo!attcan!uunet!mcvax!ukc!warwick!cvaxa!aarons
From: aarons@cvaxa.sussex.ac.uk (Aaron Sloman)
Newsgroups: comp.arch
Subject: VM needed for rapid startup
Keywords: paging virtual-memory speed
Message-ID: <463@cvaxa.sussex.ac.uk>
Date: 22 May 88 21:14:23 GMT
Organization: School of Cognitive Sciences, Univ of Sussex, Brighton, UK
Lines: 36

Several news-posters have commented on the requirement for paged virtual
memory systems (or the lack of requirement with falling costs of
memory).

There is one reason I want VM that has not been mentioned, namely that
many of the more sophisticated software packages sitting on disk are so
large that without the ability to start running after a few pages have
been read in, process start-up time is much too long.

It can be even worse if you have to read in the whole system across
ethernet. Starting up a big process from a diskless Sun PAGING over
ethernet is much faster than if the whole image had to be read in.

The argument depends on the fact that the kind of package I am talking
about has very many facilities within it with only a small, but
unpredictable, subset required for any one session of use.

Perhaps there are memory management techniques I am unaware of that
make it easy for portions of a large program to be read in as required,
without the cost of full virtual memory.

Anyhow, while disk access remains significantly slower than main memory,
something like paged virtual memory will remain highly desirable for
those of us who want to use large sophisticated software packages like
AI development environments, powerful editors, etc. EVEN if there is
enough physical memory for the whole package.

Aaron Sloman,
School of Cognitive Sciences, Univ of Sussex, Brighton, BN1 9QN, England
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As a last resort (it costs us more...)
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