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From: ml27192@uxa.cso.uiuc.edu (Mark Lanett)
Newsgroups: comp.sys.mac.system
Subject: Re: Virtual Memory and Sys 7
Message-ID: <1991May8.154845.24364@ux1.cso.uiuc.edu>
Date: 8 May 91 15:48:45 GMT
References: <1991May8.143042.20137@bigsur.uucp>
Sender: usenet@ux1.cso.uiuc.edu (News)
Organization: University of Illinois at Urbana
Lines: 30

webster@bnr.ca (Brent Webster) writes:
>I went to reconfigure my memory via the Memory control panel but it
>only allowed me to increase the memory to 11 Megs. When I rebooted my
>Mac, to my astonishment, my harddisk was short 11Megs and not the 
>3Megs plus some overhead which I expected.  I can live with that 
>but I am wishing for a more elegant solution.

There are two ways to deal with this when implementing VM: keep only extra stuff
on disk or keep a copy of everything on disk. Apple puts everything on disk
since then if a block in RAM has not been changed it does not need to be written
out to disk again.

>Running "About this Macintosh..." indicated that the System was ONLY
>taking about 1.8Meg so I figured I had 9Megs to play with.  WRONG!!!
>The "Largest Unused Block:" was about 7.2 Meg and that's all the 
>Smalltalk-80 application could see.

You do have 9 megs, but it's not contiguous. Your ROMS may be in the middle of
that space, or NuBus cards. All cards should be moved to the highest slots 
(away from the power supply) to minimize fragmentation.

>  Will I ever be able to run a 12Meg application on a Mac
>  containing 8Meg of ram?

Yes, If you run in 32-bit mode, if your machine and applications support it
(Only IIci's and later do).
--
//-----------------------------------------------------------------------------
Mark Lanett						ml27192@uxa.cs.uiuc.edu
Software Tools Group, NCSA				mlanett@ncsa.uiuc.edu