Path: utzoo!utgpu!attcan!uunet!peregrine!elroy!cit-vax!tybalt.caltech.edu!wetter
From: wetter@tybalt.caltech.edu (Pierce T. Wetter)
Newsgroups: comp.sys.mac
Subject: Re: When will MacOS get virtual memory?
Message-ID: <8218@cit-vax.Caltech.Edu>
Date: 5 Oct 88 22:59:49 GMT
References: <5624@zodiac.UUCP> <76000290@p.cs.uiuc.edu> <39513@yale-celray.yale.UUCP>
Sender: news@cit-vax.Caltech.Edu
Reply-To: wetter@tybalt.caltech.edu.UUCP (Pierce T. Wetter)
Organization: California Institute of Technology
Lines: 29

>
>Someone really should tell Sun or Apollo.  They've produced many workstations
>with 68000's running UNIX, which DOES support virtual memory and page swapping.
>Gosh, wonder how they do it?
    Supervisor mode/User Mode
>>I guess if Apple really intended to support virtual memory soon in all
>>macintoshes, then it would have put a 68020 or at least a 68010 in the
>>Mac SE.  But since most machines (SE's, Plus's) have the 68000, these
>>machines will not have virtual memory any time soon.
>
>Virtual memory doesn't REQUIRE hardware memory management.  It's a lot easier
>if you have the PMMU, but it's not impossible to do on a 68000.  Apple, though,
>probably won't bother to write its new OS for anything less than a 68020/68851
>combo... gotta keep pushing into the future, ya know!
    Nah. Supervisor mode. Read the apple list of Dont's. Such as, 
 DON"T USE SUPERVISOR MODE INSTRUCTIONS.
The new OS will undoubtably force applications to run in user mode.
Unfortunately, there are a fair number of apps which do use them.
Unfortunately, Apple probably won't seed the compiler writers with new OS 
versions before the app developers. (After all, what are you going to do if
your application was written in LSC, and LSC goes off and tweaks the status
register? Wait until LSC gets you an update.)
Pierce
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