[TUHS] Unix on PDP8?

Clem Cole clemc at ccc.com
Wed Nov 29 06:24:42 AEST 2017


On Tue, Nov 28, 2017 at 2:55 PM, Will Senn <will.senn at gmail.com> wrote:

> All,
> Was Unix ever ported to a PDP8, or any other 12 bit environment, for that
> matter?

​Not to my knowledge.

> If not, why not

​My guess ....  is that it was not worth it/did not make economic sense for

> My understanding, such as it is, is that Unix was created on the PDP7 -
> btw, thank you very much, Ken Thompson, you definitely changed my world :),
> which is an 18bit machine, and that it soon found its first real home on
> the 16 bit PDP11 series of machines (an 11/20), and from there, ever upward
> or at least ever onward. I'm curious about it for historical reasons, of
> course, but also because I've been messing around in the PDP8 emulation
> world and enjoying the excursion into simplified ISA and memory
> architectures.
> -will

Ken had borrowed a cast off 18 bit word addressed PDP-7 (which became the 9
for all intents and purposes).   They purchased a 16 bit PDP-11/20.  By
that time of the PDP-7/9 (18 bits) lines are being replaced by the PDP-10
(18/36 bits) and the 12 bit PDP-8 line, is being replaced by the 16 bit

Ken and company had tried to purchase a PDP-10 and been shot down.   So he
took the PDP-11, which they were able to get funded.   There was nothing
the 8 could do that the 11 could not do as well or better and the it was
not going to cost any more to use 11s.  So there was not incentive at BTL.
  They now have it on the 11 line.

After UNIX get released in to the wild, the same thing is happening.
Unless you had an older PDP-8 you wanted to try to run UNIX on, why
would you have ported it?   TSS/8 was cheap (ney free from DECUS IIRC) so
there was a timeshared system for the the 8s already.   You'd have have to
build new tools which is what we did for other systems, but we always
ported to a system that was giving us something -- often cheaper cycles
than the PDP-11 and getting than what we could have gotten on the packaged
system.  And PDP-11s ankle to run UNIX even at $50-250K were cheap for the

I note that the PDP-11 competitor and the other PDP-8 follow on was Ed
DeCasto's Nova.    And while Xerox clones the Nova for the Alto, I never
heard of a UNIX port to the Nova either.  DG's SW offerings were fairly

So folks like me either bought a PDP-11 from DEC and got UNIX (what most
did) and/or you might have some how need up with a cheap system that 24 or
32 bits and then you thought about porting.   Even the 'NUIX' machine (IBM
Series/1) was a case where the Cleveland State folks got the system for
super cheap.  They had a borrow cycles from Case to do the port because
they did not have an 11.

People like me did not start to "port" UNIX until the 16 bit micro's show
up -- i.e. the 68000, Z8000, 8086 where you could build a 'microcomputer'
that was close to the power of the 'minicomputer' for a lot less money.

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