> The 68010 and 68020 had it as another chip. Motorola sold an MMU to go along
> with the processor, but Sun didn't use it. They rolled their own. I believe
> that's correct, or I'm blind as a bat (I couldn't find an MMU
> on my 3/60).

I think the Sun2 came out before the PMMU came out; the original Motorola
MMU (68451?) was a completely misdesigned nightmare, and lots of companies
rolled their own instead of it.  I'm pretty sure the 68020 and 68851 were
contemporary, but Sun may have stayed with their original design to speed
the porting effort.  (It may also have been faster; the 68851 is a complex
beast and adds more wait cycles than it's really entitled to. :-) )