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From: stew@endor.harvard.edu (Stew Rubenstein)
Newsgroups: comp.sys.mac
Subject: Re: Virtual Memory with the Mac OS
Message-ID: <2929@husc6.UUCP>
Date: Sun, 4-Oct-87 12:21:29 EDT
Article-I.D.: husc6.2929
Posted: Sun Oct  4 12:21:29 1987
Date-Received: Wed, 7-Oct-87 05:44:34 EDT
References: <2653@okstate.UUCP> <2542@batcomputer.tn.cornell.edu>
Sender: news@husc6.UUCP
Reply-To: stew@endor.UUCP (Stew Rubenstein)
Organization: Aiken Computation Lab Harvard, Cambridge, MA
Lines: 25
Keywords: virtual memory 68851

>In article <2653@okstate.UUCP> norman@a.cs.okstate.edu (Norman Graham) writes:
>>Does anyone out there know what it would take to have demand paging virtual 
>>memory on the Mac II?  Could it be as simple as plugging in a 68851 and 
>>writing an interrupt handler to take care of swapping the pages?

In article <2542@batcomputer.tn.cornell.edu> chow@tcgould.tn.cornell.edu (Christopher Chow) writes:
>One thing which you might want to question is whether if you want to add an
>68851 MMU to your Mac II.  I'm not a hardware guru, but from what
>understand, the 68851 chip adds wait state(s) to every memory reference.

The wait states are already there.  Two of 'em.  The 851 doesn't add any more.
As I understand it, it's a drop-in replacement for the fake MMU that's in
there now.

I don't think that interrupt handler is so simple.  You also have to worry
about getting the page map set up to begin with, and a million other things.
I am sure Apple is working on it, and I hope they've hired some folks who
know something about multi-user operating systems.  They've said that the
Multifinder we are seeing now is just the first generation in an evolution
towards real multi-tasking.

Stew Rubenstein
Cambridge Scientific Computing, Inc.
UUCPnet:    seismo!harvard!rubenstein            CompuServe: 76525,421
Internet:   rubenstein@harvard.harvard.edu       MCIMail:    CSC