[TUHS] Unix use of VAX protection modes

[Warner Losh via TUHS]

On Wed, Jan 21, 2026 at 8:52 AM Warner Losh <imp at bsdimp.com> wrote:

>
>
> 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...
>

The AI chat bots seem to think this paper was

"A High Performance X Server for a 64-bit Architecture," presented by
Silicon Graphics at the 8th X Technical Conference in 1994,

But I can't find it online... Anybody know a source?

Warner