Motorola Unix Port

[Mike Lutz]

Just for the record, the Tropel Division of GCA has UNIX(*) running on
the same EXORMACS based system as the Motorola port.  The difference is
that they started from V7 (well before System V was announced), but
have added lots of goodies from System III/V and the Berkeley
distributions since then.  Also, they are not plagued with performance
spikes at each process switch.

Yes, the EXORMACS MMU is a bash & bound unit with translation disabled
in supervisor mode.  This is a real loss for UNIX, as the kernel
implicitly assumes that the current process context is mapped onto
fixed kernal space addresses.  From what I've been able to gather,
Motorola *simulates* mapping by constantly copying context information
into and out of a fixed buffer area -- obviously an expensive
operation.

The "tropix" design does *not* involve the huge 4 millisecond process
switch overhead nor 2 milliseconds at spl7 because most of the kernel
runs in *user* mode, so mapping is available.  Reference the paper by
Mike Shon & me in the July 1983 USENIX Proceedings.

Mike Lutz

(*) UNIX is a Trademark of Bell Labs
-- 
Mike Lutz	Rochester Institute of Technology, Rochester NY
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