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From: philip@pescadero.Stanford.EDU (Philip Machanick)
Newsgroups: comp.sys.mac.system
Subject: Best way of doing VM? (was Re: SE/30 VM trouble in System 7)
Message-ID: <1991May29.201759.6433@neon.Stanford.EDU>
Date: 29 May 91 20:17:59 GMT
References: <2842d41f.4648@petunia.CalPoly.EDU> <1991May29.125650.16389@zardoz.eng.ohio-state.edu>,<53439@apple.Apple.COM> <1991May29.173052.17108@zardoz.eng.ohio-state.edu>
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In article <1991May29.173052.17108@zardoz.eng.ohio-state.edu>,
gaynor@agvax2.ag.ohio-state.edu writes:
|> From this, it would appear that Virtual Memory, even in small
|> portions, would require -huge- amounts of disk space for those with
|> large amounts of RAM.

Minor point on terminology: virtual address space means the
whole thing, not just what is stored on disk. I don't know
why Apple has chosen to store the entire virtual address
space on disk - perhaps someone from Apple would care to
comment.

I can list a few possible reasons for doing this, but none
apply immediately (is Apple perhaps thinking ahead...?):

o mapping files to memory - this is a useful technique
  and is a relatively simple generalization if all of VM
  is stored on disk
o process migration - in a multiprocessor machine, it is
  relatively easy to move a process to another processor
  if all of VM is on disk
o it's easier to manage multiple address spaces on
  the same machine - you just allocate each exactly the
  amount of disk space needed for its VM
-- 
Philip Machanick
philip@pescadero.stanford.edu