[TUHS] Unix use of VAX protection modes

[Rich Salz via TUHS]

On Wed, Jan 21, 2026 at 9:51 AM Larry McVoy via TUHS <tuhs at tuhs.org> wrote:

> 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.


 Apollo did something similar.  If the first CPU faulted, the second would
halt it, page in the memory and restart the first one.