Newsgroups: comp.sys.mac.system
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From: gillies@m.cs.uiuc.edu (Don Gillies)
Subject: Re: VM rule of thumb (sic)
Message-ID: <1991May30.193537.21239@m.cs.uiuc.edu>
Organization: University of Illinois, Dept. of Comp. Sci., Urbana, IL
References: <1991May30.132055.23209@xn.ll.mit.edu> <14845@ector.cs.purdue.edu>
Date: Thu, 30 May 1991 19:35:37 GMT

My own rule of thumb gleaned from Pilot (Xerox OS) is also 2:1.  Thus
this rule is not just a UNIX artifact.  I think that most reasonable
systems, when the software is packaged/tuned for VM, can present
double the amount of physical memory without thrashing.

128Mb of virtual memory v.s. 8Mb of physical memory on a LISP machine
is because LISP is a joke.  Common Lisp has thousands of useless
functions that need to be available, and are eating that swap space.
You have other junk in your environment like a compiler or a debugger
that by all rights is wasting VM 100% of the time.  And the majority
of garbage collection algorithms are dogs if memory is more than 50%
occupied.

So while you *say* you have 128Mb of virtual memory, you are probably
*using* tons less memory, the rest being garbage of one sort or
another.  Too bad for you, great for the disk drive makers.

Don Gillies	     |  University of Illinois at Urbana-Champaign
gillies@cs.uiuc.edu  |  Digital Computer Lab, 1304 W. Springfield, Urbana IL

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