[TUHS] A PDP-10 used for UNIX just after the PDP-7?

[Ken Thompson via TUHS]

except for porting and testing, i didnt use the
pdp-9s or -15s. the pdp-7 could support 2 people
while the others only had tty33. also the pdp-7
had the filesystem with all the current work.

the ks-11 was the first memory protected pdp-11.
we needed it to pretend like it was a real time
sharing system. ks was the dec designation
for a one-of-a-kind. dec did a lot of special
system designs for customers. there is a
computer, i think pdp-2, that was a completely
custom built  computer.

On Thu, Jan 15, 2026 at 11:12 PM Thalia Archibald <thalia at archibald.dev>
wrote:

> On Jan 15, 2026, at 23:57, Ken Thompson wrote:
> > after the pdp-7, unix was ported to more
> > stock pdp-9 and pdp15 (both pdp7 upgrades)
> >
> > no pdp-10 at bell labs.
>
> Hi Ken,
>
> So the "PDP-10" that Mahoney refers to is the PDP-11 with KS-1 memory
> management? Seems like a strange machine.
>
> And did you only ever use the one PDP-7 from the graphics group, and the
> other
> PDP-9s and 15s were used by other groups?  Warner Losh writes that the
> PDP-7
> UNIX “Total install base was 4 (1 pdp-7, 2 pdp-9 and 1 pdp-15)”.
>
> https://papers.freebsd.org/2020/fosdem/losh-hidden_early_history_of_unix/
>
> Thalia
>