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

[Ken Thompson via TUHS]

after the pdp-7, unix was ported to more
stock pdp-9 and pdp15 (both pdp7 upgrades)

no pdp-10 at bell labs.


On Thu, Jan 15, 2026 at 10:54 PM Thalia Archibald via TUHS <tuhs at tuhs.org>
wrote:

> In Mahoney's oral history, he writes that after the PDP-7, "The file
> system was
> then put on a PDP-10". And in Thompson's 1989 interview with Mahoney, he
> mentions that "Before the 11/45 was available we bought a PDP-11 that had
> PDP-10
> memory management, KS-1, it was a one of a kind machine".
>
> Are these the same system? I've never seen any other references to a
> PDP-10 used
> in early UNIX development, only that their request for a 10 was denied.
> Does
> anyone know anything about this strange PDP-11 + KS-1?
>
> What was the model of PDP-11 first used for UNIX? What hardware was sold
> by the
> UNIX group to the patent department? I presume it was an 11, since the 7
> was
> never their property.
>
> Mahoney's words:
>
>     When Thompson realized that the PDP-7 was not powerful enough to
> implement a
>     file system that could offer some of the advantages of Multics he
> initially
>     programmed a bare-bones file system. The file system was then put on a
>     PDP-10. Using this enhanced capability, Thompson and the others slowly
> added
>     tools that helped them monitor what the file system was doing. Thompson
>     devoted a month apiece to the shell, editor, assembler, and other
> software
>     tools. When asked when he realized that a new operating system was
> being
>     born, Thompson replied,
>
>
> https://dspinellis.github.io/oral-history-of-unix/frs122/unixhist/finalhis.htm
>
> My summarization of the relevant paragraphs of Thompson's 1989 interview:
>
>     After the PDP-7 was at the end of its life, they needed a new machine,
> so
>     they proposed to buy a PDP-11 model that was about to be announced. The
>     proposal was rejected, but the psychology research department decided
> to buy
>     it and give it to them. They placed the new PDP-11 in Osanna's office
> next
>     to the PDP-7 and wrote cross tools. They wrote a PDP-11 assembler on
> the 7
>     in B and ran the paper tape across the floor to the 11. For its first
> month,
>     the 11 was without a disk, so they had a fake in-memory filesystem.
> Once it
>     was delivered, they got UNIX running on it in about a week and, at this
>     point, the topology of the directory structure was rather fixed.
>
>     When the patent department was about to buy AstroText, a horrific and
>     expensive typesetting package, they instead produced a version of
>     nroff/troff for their specific formatting needs. They also talked the
> patent
>     department into buying their system, i.e., the physical hardware, and
> moving
>     it out. With that money, they bought an 11/45. Before the 11/45 was
>     available, they bought a PDP-11 that had PDP-10 memory management,
> KS-1, a
>     one-of-a-kind machine. This was the first time they were using the
> machine
>     at the same time for program development as typists.
>
>
> https://dspinellis.github.io/oral-history-of-unix/mike/transcripts/thompson.htm
>
> Thalia
>