Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!cs.utexas.edu!sun-barr!sun!hanami!landman
From: landman%hanami@Sun.COM (Howard A. Landman)
Newsgroups: comp.sys.mac
Subject: Re: Virtual Memory and hard disk life
Keywords: Virtual Memory
Message-ID: <109873@sun.Eng.Sun.COM>
Date: 14 Jun 89 00:43:16 GMT
References: <13548@ut-emx.UUCP>
Sender: news@sun.Eng.Sun.COM
Reply-To: landman@sun.UUCP (Howard A. Landman)
Organization: Sun Microsystems, Mountain View
Lines: 23

In article <13548@ut-emx.UUCP> osmigo@ut-emx.UUCP writes:
>It seems to me that if you used Virtual Memory as your "standard, everyday
>setup," it would involve INSTENSE, CONTINUOUS hard disk accessing, in contrast
>to the occasional "chirp" of the drive we now experience.

No, it only involves disk accessing when you want to read or write something
and it's not in memory.  That means a "page fault".  With enough memory, or a
program that doesn't really use all the memory it has allocated, you just
don't page fault that often.

In a non-virtual system, you MUST have everything in memory at all times
(unless there's some other form of swapping to disk), so if you need just
a little more, BANG you're dead.  Virtual allows you to organize your
program in the simplest way without having to deal with such messy issues
except in the general sense of trying not to use memory too wastefully.
And if you overstep the limit, it degrades relatively gracefully - it runs
slower, but it still runs.

Virtual memory is like growing old - it doesn't seem so bad when I consider
the alternatives ...

	Howard A. Landman
	landman@sun.com