[TUHS] Unix use of VAX protection modes

[Larry McVoy via TUHS]

On Tue, Jan 20, 2026 at 06:08:09PM -0800, Erik E. Fair via TUHS wrote:
> Clem, do you want to chime in here to describe MassComp's extravagant
> solution to that?

I think I sort of know what they did. They ran 2 68k cpus in lock step,
with one some number of instructions behind.  When the leading CPU
faulted, it stopped the other one before it ran the instruction that
faulted, the stopped one somehow was redirected to handle the fault.

I feel like Forest Baskett may have been involved in that idea, maybe
he did it first elsewhere?  Anyone know?

Clem will chime in with the correct details.