On Tue, Jul 25, 2000 at 02:53:55PM -0800, Grant Stockly wrote:
> >There was a discussion some time ago (see http://mail-index.netbsd.org for
> >archives), if I remember properly the conclusion was that most i960-based
> >systems availanle didn't have an MMU, and so were unusable for an Unix-like
> >system.
> 
> What exactly is the function of an MMU and can it be emulated in software?

An MMU is a Memory Management Unit. Typical MMU functions include the
ability to reference a Virtual Memory address space, and have the MMU
trigger an interrupt when a process tries to access something that isn't
available in RAM at the moment - then you catch that interrupt and load
the required data and the process can continue. MMUs also provide the
ability to trap regions of memory so that a process can be denied access
to memory that doesn't belong to it.

So no, you can't emulate it in software. If the CPU supported catching
the operations described above so that software could do some of the work,
it would arguably have a 'built-in' MMU.

-- 
David Maxwell, david@vex.net|david@maxwell.net --> Mastery of UNIX, like
mastery of language, offers real freedom. The price of freedom is always dear,
but there's no substitute. Personally, I'd rather pay for my freedom than live
in a bitmapped, pop-up-happy dungeon like NT. - Thomas Scoville