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From: MRC%PANDA@SUMEX-AIM.ARPA (Mark Crispin)
Newsgroups: net.micro.atari
Subject: Unix without an MMU
Message-ID: <12173015456.10.MRC@PANDA>
Date: Mon, 6-Jan-86 03:51:02 EST
Article-I.D.: PANDA.12173015456.10.MRC
Posted: Mon Jan  6 03:51:02 1986
Date-Received: Tue, 7-Jan-86 04:17:01 EST
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Organization: The ARPA Internet
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     Instead of flaming about whether or not Unix* can run
without memory management, why not examine the actual problem.
Bringing up whether or not OS-9 can run without an MMU is silly.
That's like saying that since both wood and gasoline burn, you
can put logs in your car's gas tank.

     Most people consider Unix to comprise a full Unix
environment including all the system services and multiprocess
facilities provided by a Unix system.  In other words, a shell
and some package that emulates Unix system calls is *not* Unix.
If you have multiple processes running in a non-memory managed
system, you are restricted to one of the following:
 . each process absolute-assembled into a different partition of
   memory (ala DEC RSX-11)
 . only one process in memory at a time -- each process swapped
   out when it blocks or its quantum expires
 . all software assembled to perform all memory references
   indexed by a base register, which is loaded by the operating
   system and which the program must not change (ala old IBM OS)

     These are big problems.  Remember, anybody can write
software that does 90% of what Unix does without any of these
problems.  It's called CP/M or MS-DOS or DOS-II or GEM or TOS or
OS/A+ or...ad nauseum.  It's that last 10% that's difficult.

     To be honest, I believe it is more economical to upgrade an
ST to have an MMU than to do the required software hacking.  What
about the license cost?  Gee, I'd think if you are going to fork
over for a Unix license you might as well get a more competant
engine to run it!

     This isn't to say that some clever individual couldn't
do something about "Unix for the ST".  I'd suspect that what
would be presented is a Unix-lookalike environment with some
shell and the Unix system calls, but not a real Unix.  It's that
last 10% all over again...

-- Mark --

* Unix (TM) is a trademark of Bell Labs to describe the
absolutely terrible operating system they have conned large
segments of the computer industry to adopt simply because there
is no other portable operating system with the necessary
facilities.  It also describes the philsophy of those individuals
who wish to make computers mysterious to the general public again
after 20 years of effort to make computers understandable.
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