Path: utzoo!censor!geac!jtsv16!uunet!samsung!usc!polyslo!rcfische
From: rcfische@polyslo.CalPoly.EDU (Raymond C. Fischer)
Newsgroups: comp.sys.mac.hardware
Subject: Re: Looking for a reason to install my PMMU
Message-ID: <1989Nov14.211328.21066@polyslo.CalPoly.EDU>
Date: 14 Nov 89 21:13:28 GMT
References: <7450@sdcsvax.UCSD.Edu>
Reply-To: rcfische@polyslo.CalPoly.EDU (Raymond C. Fischer)
Distribution: usa
Organization: Cal Poly State University -- San Luis Obispo
Lines: 32

In article <7450@sdcsvax.UCSD.Edu> rfellman@ucsd.edu (Ronald D. Fellman) writes:
>I have a Motorola XC68851 RC16 PMMU and a MacII loaded with 5 Megs of
>RAM.  Is there any GOOD reason to plug in the PMMU given that I almost 
>never run out of RAM? I am therefore not interested in the RAM disk
>program. As I understand it, the 6.0.3 version of the operating sys
>couldn't care less about PMMUs.  Why, therefore is there SO much fuss
>about PMMUs?

Because virtual memory is the latest fad in the Mac world and everyone
is jumping on the bandwagon.  Consider ...

System 7 is not here yet.  Real memory is $80/meg.  Disk storage is
$10 to $15 per meg.  A PMMU is $200.  Virtual memory is slower than
real memory.  If _you_ want 8Mb, then the cost is ...

Real: $80x4=$320 (1Mb SIMMs)
	 $-20x4=$-80 (old 256k SIMMs)
	 -----------
			$240 (Total for 8Mb real)

Virtual:    $200    (PMMU)
	   $12x8=$96    (disk space)
	   ---------
		    $296 (Total for 8Mb virtual)

I have 5Mb of memory in my SE/30 and although the 68030 in it can 
handle demand paged virtual memory, I'm not likely to use it because 
1) 5Mb is enough, and 2) I don't have 8 or 16 Mb of free disk space 
to use for paging.

Ray Fischer
rcfische@polyslo.calpoly.edu