Subject: Re: None
To: None <amiga@NetBSD.ORG>
From: Michael van Elst <>
List: amiga
Date: 12/03/1995 22:58:22 writes:

>	No such luck.  They had some form of MMU on it.  The 68000 was
>designed to run things like unix.

No. The 68000 does not support (transparent) virtual memory because
a page fault cannot be handled for every user-mode instruction.
The 68010 extended the bus-error exception so that any user-mode
instruction could be continued where it was aborted.

I believe the Sun-2 used 68010s.

It is possible to do VM on the 68000 if you avoid certain
instructions. You also need to emulate some instructions
in the page-fault handler.

>The innovation of the 68020 was to
>more tightly couple the MMU to the CPU.

Sort of. The main difference was that you could make an MMU a
coprocessor instead of a peripheral. Regarding implementation
of virtual memory there is no difference to the 68010.

>However, there is nothing
>stopping you from inventing an MMU for any CPU.

The MMU is not the problem. But for transparent VM you need to
be able to restart or continue any user-mode instruction.

>At any rate, the
>Amiga doesn't have one.

Could you explain this theory ? :)

                                Michael van Elst

                                "A potential Snark may lurk in every tree."