Actually not in lock step. They were independent. One was called the executor and the other the fixer. When a fault was detected the executor was sent wait stated while the fixer handled the fault and refilled the TLB. Once the TLB was set to instruction was allowed to complete. Btw when the 68010 was released the pals on the board were changed to allow the executor to actually take the fault and do something else while the fixer replaced the TLB entry

The idea was proposed by Forest Baskett at an early Asilomar conference but never built by him - I want to say 1980 or 81. I have lost that paper and would love to find a copy again BTW. To be fair both Apollo and Masscomp’s hw teams reduced the idea to practice independently but I know of no other folks that tried it.

On Fri, Aug 30, 2019 at 5:52 PM Larry McVoy <lm@mcvoy.com> wrote:

On Fri, Aug 30, 2019 at 04:39:09PM -0400, Clem Cole wrote:
> MC-500/DP was the first MP Unix >>product<< -- predates our friends in on
> the West coast by 2 years).

And as I recall you had to do 2 68000's in lockstep to get the VM system
to do page fault restarts. That was neat, was that a Masscomp invention
or was it a commonly known trick?

--lm

Sent from a handheld expect more typos than usual