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From: ddj@zardoz.club.cc.cmu.edu (Doug DeJulio)
Newsgroups: comp.sys.next
Subject: Re: Mac Software on a NeXT ???  PLEASE!!
Message-ID: <1991May30.171743.16463@cs.cmu.edu>
Date: 30 May 91 17:17:43 GMT
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In article <1991May29.174221.14752@wam.umd.edu> mikec@wam.umd.edu (Michael D. Callaghan) writes:
>One of the biggest problems was the fact that the Mac OS wants complete
>control of the computer. Unix doesn't seem to care for that. Apparently,
>in order for the Mac Emulator to work, it would have to kick out the NeXT
>OS completely. Who wants that?

You wouldn't need to kick out the NeXT OS completely.  You *would*
probably need to modify the kernel.

My understanding is that all recent 68k series chips ('040, '030,
maybe '020) have support for providing supervisor mode *emulation*, by
trapping the instructions that are used to enter and use supervisor
mode (like the 040 does with floating point operations it can't do in
hardware).  When a process without permission tries to enter
supervisor mode, a trap is generated and the kernel can do anything it
wants, including creating the illusion that the instruction worked.
One could create a software environment that was an entire virtual
machine, from the point of view of a given process.  It should be
theoretically possible to run a Macintosh in a single NeXTstep window.
It might even be possible with enough work to run mac apps as separate
NeXTstep windows, but I don't think it'd be worth the extra effort.
Something like Mouse-X (hot key to switch between screens) would be
just right for me.
-- 
Doug DeJulio
ddj@zardoz.club.cc.cmu.edu