>>>>> "John" == John E Clark <jclark@synergy.encinitas.ca.us> writes:

John> If the CPU is in fact a 68000/10 then the only type of 'swaping'
John> is full task swapping, ie no paging. I don't know if BSD was
John> ever envisioned for a purely swaping environment. However,
John> SYSV-mumble-foo, and V6 un*x were.

I know my computer engineering prof built a 68010 based computer with
own developped memory management hardware which he ported BSD to.  All
this was a toy project of his and never released.  However it did
work.

John> The problem with 'paging' is that the 68000 couldn't restart
John> instructions, so if the task wasn't fully in memory then a bus
John> error on a non-existent/paged memory area would cause the task
John> to fault out.

Well, there are ways to cheat, I think Appollo had a design with two
68000's one instruction out of sync with each other.  When the first
trapped on an illegal memory access the MM hardware brought in the
page and then the processors roles were switched so that the untrapped
processor could continue the process.  Neat no?  The 68010 could
restart instructions.  That was one of the reasons it existed.

Niklas

Niklas Hallqvist	Phone: +46-(0)31-40 75 00
Applitron Datasystem	Fax:   +46-(0)31-83 39 50
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