[TUHS] Unix use of VAX protection modes

[Warner Losh via TUHS]

On Tue, Jan 20, 2026 at 12:48 PM Paul Winalski via TUHS <tuhs at tuhs.org>
wrote:

> My question is, did Unix make any use of either supervisor or executive
> mode on the VAX?
>

I know that SGI did use these modes on the MIPS processor. But it was a bit
like
the 2.11BSD use: They created supervisor mode code for the X server that
anybody
could call, but mediated the access to the hardware to trusted code. They
did this as
part of their protocol optional interface to the hardware since 80% of the
time was chewed
up in protocol things, at least according to a presentation I saw / paper I
read about
it at one of the X technical conferences. They did this generically to
allow a richer interface
to devices than a driver could normally provide to userland, as well as
hopping on the
microkernel bandwagon. It was a good idea, though, since this was basically
just a process
that ran in a different processor mode, so it was easy to restart if it
crashed...

Warner