Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!bloom-beacon!mit-eddie!ll-xn!ames!lll-tis!daitc!jkrueger
From: jkrueger@daitc.ARPA (Jonathan Krueger)
Newsgroups: comp.arch
Subject: Re: Today's dumb question...
Message-ID: <53@daitc.ARPA>
Date: 13 May 88 15:53:29 GMT
References: <503@xios.XIOS.UUCP> <2676@pdn.UUCP> <674@cernvax.UUCP> <9558@sol.ARPA>
Reply-To: jkrueger@daitc.UUCP (Jonathan Krueger)
Organization: Defense Applied Information Technology Center, Alexandria VA
Lines: 25

>In article <674@cernvax.UUCP> hjm@cernvax.UUCP (Hubert Matthews) writes:
>>	- virtual memory is useful only when an application won't fit in
>>	  physical memory.  But memory is cheap, so with lots of Mbytes
>>	  who needs it, especially if the program is written well.

In article <9558@sol.ARPA> crowl@cs.rochester.edu (Lawrence Crowl) writes:
>Here are some counter-examples.  Others can provide more.

Two more:

avoiding memory fragmentation - virtual memory management provides a
way for multiple processes to share the physical store, cleanly and
without performance bottlenecks.  New processes start and grow all the
time, multiple requirements for space vary dynamically, each is
satisfied efficiently to the limits of available physical memory.
Even when physical memory is cheap, processor time to manage it is
not.

preventing unnecessary i/o - virtual memory systems need not load in
an entire image, thus performing fewer disk-to-memory reads per
execution, an advantage in a development cycle, among other places.
Even when physical memory is cheap, i/o bandwidth to fill it with
stuff copied from disk is not.

-- Jon