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From: ml27192@uxa.cso.uiuc.edu (Mark Lanett)
Newsgroups: comp.sys.mac.system
Subject: Re: Virtual Memory and Disk Usage
Message-ID: <1991May28.183010.20752@ux1.cso.uiuc.edu>
Date: 28 May 91 18:30:10 GMT
References: <1464@mephisto.edu>
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Organization: University of Illinois at Urbana
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ashwin@gatech.edu (Ashwin Ram) writes:

>1. When I turn on virtual memory on my IIsi, my disk usage (as indicated by
[...]
>   Is this normal?  I can see that the straightforward way of implementing
>   virtual memory would be to allocate 9Mb of disk space, and treat the RAM
>   as a 5Mb cache so that 5Mb of the 9Mb would be paged into main memory at
>   any given time.  However, an alternate (and not much more complex) scheme
>   would need only 4Mb plus one page (1k or whatever the page size is) on
>   disk.  When needed, the system would swap a page out and then read the
>   requested page in.  (This scheme requires less disk but may involve extra
>   disk writes if >5Mb is in use and a clean page needs to be swapped out.)

You are correct in your thinking. However, your "not much more complex" 
method is used by nobody since it requires almost twice as many writes. Apple
is doing it just like everybody else this time.

>-- Ashwin.
--
//-----------------------------------------------------------------------------
Mark Lanett						ml27192@uxa.cs.uiuc.edu
Software Tools Group, NCSA				mlanett@ncsa.uiuc.edu
I'm not an idiot; I just play one on the net.