Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!apple!ames!purdue!mentor.cc.purdue.edu!ags
From: ags@mentor.cc.purdue.edu (Dave Seaman)
Newsgroups: comp.sys.mac
Subject: Re: Virtual Memory and hard disk life
Keywords: Virtual Memory
Message-ID: <2877@mentor.cc.purdue.edu>
Date: 2 Jun 89 19:15:42 GMT
References: <13548@ut-emx.UUCP> <2872@cadre.dsl.PITTSBURGH.EDU> <10954@orstcs.CS.ORST.EDU>
Reply-To: ags@mentor.cc.purdue.edu (Dave Seaman)
Organization: Purdue University
Lines: 23

In article <10954@orstcs.CS.ORST.EDU> flatmas@ladder.CS.ORST.EDU (Scott Timothy Flatman) writes:
>Virtual memory has to constantly switch pages in and out of memory.

Not true, as any NeXT user can testify.  When there is page swapping going on
on my NeXT, I can hear the disk activity.  Right now, as I type this, there is
only the motor hum.  That means that the disk is rotating, as always, but there
are no reads or writes.  That's not surprising, because I have no
memory-intensive background processes (such as Mathematica) running now, and it
does not take 8 megabytes to run a terminal window.

Depending on your usage patterns, virtual memory may lead to less disk usage,
rather than more.  If I am running Mathematica on my NeXT and I want to do
something else, there is a brief clatter of disk activity as Mathematica is
swapped out to make room for another process.  When I go back to Mathematica,
there is another brief clatter as pages are swapped back in.  The total amount
of disk activity in swapping Mathematica out and back in again is far less
than what it would take to re-launch Mathematica from scratch and fire up the
kernel again.  By contrast, that is exactly what I have to do when I run
Mathematica on my Mac II, using a 4 Mb Multifinder partition on a 5 Mb
machine.  There is hardly anything other than the finder that is small enough
to run while Mathematica is active, so I have to kill it and re-launch it
whenever I need to do something else.  This causes a lot of unnecessary
activity on my Mac disk.