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From: siegel@world.std.com (Rich Siegel)
Newsgroups: comp.sys.mac.programmer
Subject: Re: System 7.0/Supervisor Mode ?
Message-ID: <1991May15.024320.9727@world.std.com>
Date: 15 May 91 02:43:20 GMT
References: <10972.282FE0AB@stjhmc.fidonet.org>
Organization: Symantec Language Products Group
Lines: 30

In article <10972.282FE0AB@stjhmc.fidonet.org> Lawson.English@p88.f15.n300.z1.fidonet.org (Lawson English) writes:
>Brian Kendig writes in a message to All
>
>BK> How difficult a modification would it be to have my SE use user 
>BK> mode, too? Is this a matter of a simple INIT that would just 
>BK> toss my machine into user mode without worrying about VM, or 
>BK> am I talking about something that would require a major rewrite 
>BK> of the operating system here?

	It's trivial to do, since it only involves changin a single bit
in the status register, and it'll only break software that depends on
exception stack frames, but it's a completely useless thing to do on
a Mac SE, which is neither pre-emptive nor is it capable of supporting
an MMU directly.

>Speaking sans true knowledge (as is my wont), I'd guess that "32-bit clean"
>is the telling factor as to whether supervisor or user mode is to be used-if
>an application is 32-bit clean, then the OS developers probably assumed that
>it would be following the rest of Apple compatibility guidelines.

	Actually, the deciding factor is whether the user turns on
"Virtual Memory" in his control panel. The machine still runs in supervisor
mode in 32-bit mode when VM is off.

R.
-- 
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Rich Siegel                              Internet: siegel@world.std.com
Software Engineer                        Applelink: SIEGEL
Symantec Languages Group