Path: utzoo!news-server.csri.toronto.edu!cs.utexas.edu!uwm.edu!psuvax1!psuvm!jkt100
From: JKT100@psuvm.psu.edu (JKT)
Newsgroups: comp.sys.amiga.emulations
Subject: Re: Emulator Mechanics
Message-ID: <91070.232339JKT100@psuvm.psu.edu>
Date: 12 Mar 91 04:23:39 GMT
References: <1991Mar7.093149.18707@mintaka.lcs.mit.edu>
 <19749@cbmvax.commodore.com> <1991Mar12.011418.24768@mintaka.lcs.mit.edu>
Organization: Penn State University
Lines: 53

>>> Why doesn't AMAX multitask? It should be EASY to run multiple copies
>>>of the Mac ROM as a task (since its a rom, its mostly pure code...)

Well, it's pure code that is not prepared to share ANY memory locations
with other tasks...

>>Without massive patching of the Mac ROM, I don't think so.  The same reason
>>you don't have more sophisticated multitasking on the Mac itself.  You can't
>>run multiple copies of the same Mac ROM code, since the code is not reentrant
>>like Amiga code.  Without some clever MMU tricks, I don't think you could
>>easily relocate things such that several different copies of the ROM code
>>could coexist.

At least one person has posted here to c.s.a.? saying he's tried and
nearly gotten working a Mac emulator that multitasked with AmigaDOS.
Problem is, he sacrificed a LOT of compatibility and speed to do it.
ie. What he ended up with wasn't very viable.

>>Apple does seem to have decent technical folks, I doubt they missed
>>any easy tricks...
>
>Well  it's not a heavy loss if you can't make the Mac ROM resident, but
>why does AMAX have to take over the Amiga's operating system? The only
>thing that would make it really diffcult to run MacOS under
>AmigaDOS is if Mac code fiddles with absolute memory locations or the
>OS implements function calls as traps/interupts.

Mac OS code does a LOT of stuff that would be considered illegal in
Amiga code.  But can you blame it?  It was designed under the assumption
that it owned the machine; and on any real Mac it does.  It *is* the
operating system, after all!  ;-)

>I also wonder why readysoft used a special disformat for Mac disks
>instead of reading Amiga disks.

ReadySoft did a lot of things that may seem strange, but they did
them in the name of speed and compatibility.  With the disks, you
have to understand that the Mac uses a mighty strange disk format.
Mac drives are even variable speed.  ReadySoft created a special
disk format for compatiblity with disk I/O routines that expected
a Mac floppy.  And I congratulate ReadySoft on their achievement.
I have been able to sector-edit A-Max format floppies and run
Norton Utilities on them, all without ANY problem.  Kudos!!

                                                            Kurt
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