Path: utzoo!utgpu!water!watmath!clyde!att-cb!att-ih!pacbell!ames!ncar!boulder!sunybcs!bingvaxu!leah!itsgw!nysernic!cmx!batcomputer!chow
From: chow@batcomputer.tn.cornell.edu (Christopher Chow)
Newsgroups: comp.sys.mac
Subject: Re: A/UX window systems, Mac toolbox, etc
Keywords: Macintosh multitasking
Message-ID: <4267@batcomputer.tn.cornell.edu>
Date: 31 Mar 88 17:45:33 GMT
References: <283@rhesus.primate.wisc.edu> <1710@ssc-vax.UUCP> <7593@apple.Apple.Com> <3609@bloom-beacon.MIT.EDU> <7670@apple.Apple.Com> <7681@agate.BERKELEY.EDU> <270@cantuar.UUCP>
Reply-To: chow@tcgould.tn.cornell.edu (Christopher Chow)
Organization: Cornell Theory Center, Cornell University, Ithaca NY
Lines: 27

In article <270@cantuar.UUCP> james@cantuar.UUCP (J. Collier) writes:
>
>   [...]
>   Unfortunately, the Mac Toolbox/OS falls down twice:
>1) the processor is *always* in supervisor mode

One thing I always wanted to know -- why did and why do all Macintoshes
running under the Macintosh OS always run in supervisor mode, (especially
when Apple guidelines prohibits using certain priveleged instructions such
as RTE)?

Perhaps the original decision to run in supervisor mode may have to do with
the limited amount of RAM avalible on the classic 128k Mac (since the
supervisor state has its own stack, ...).  But if lack of memory was the
only problem then this could have been changed with either the 512k 'fat'
Mac or especially the Mac Plus since it had a new set of ROMs anyway.

Comments solicited...

Christopher Chow
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