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From: (Noel Chiappa)
Subject: Re: [TUHS] Unix for PDP11/20 w/o mmu or paging option
Date: Fri, 17 Sep 2021 11:35:23 -0400 (EDT)	[thread overview]
Message-ID: <> (raw)

    > From: Roland Huisman

    > I have a PDP11/20 and I would love to run an early Unix version on
    > it. ... But it seems that the earliest versions of Unix do not need the
    > extra memory.  Does anyone have RK05 disk images for these early Unix
    > versions?

Although the _kernel_ source for V1 is available:

most of the rest is missing; only 'init' and 'sh' are available. So one would
have to write almost _everything_ else. Some commands are available in PDP-11
assembler in later versions, and might be movable without _too_ much work -
but one would have to start with the assembler itself, which is luckily in

If I were trying to run 'UNIX' on an -11/20, I think the only reasonable
choice would be MINI-UNIX:

It's basically V6 UNIX with all use of the PDP-11 memory management
removed. The advantage of going MINI-UNIX is that almost all V6 source
(applications, drivers, etc) will run on it 'as is'.

It does need ~56KB of main memory. If you don't have that much on the -11/20,
LSX (links in the above) would be an option; it's very similar to MINI-UNIX,
but is trimmed down some, to allow its use on systems with less main memory.

I'm not sure if MINI-UNIX has been run on the -11/20, but it _should_ run
there; it runs on the -11/05, and the only differences between the /20 and the
/05 are that the /20 does not have the RTT instruction (and I just checked,
and MINI-UNIX doesn't use RTT), and SWAB doesn't clear the V condition code
bit. (There are other minor differences, such as OP Rn, (Rn)+ are different on
the -11/20, but that shouldn't be an issue.)

Step 1 would be to get MINI-UNIX running on an -11/20 under a simulator; links
in the above to get you there.


             reply	other threads:[~2021-09-17 15:55 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-17 15:35 Noel Chiappa [this message]
2021-09-17 18:28 ` Phil Budne
2021-09-17 19:43   ` Clem Cole
2021-09-17 19:51     ` Brantley Coile
2021-09-17 20:07       ` Clem Cole
2021-09-17 21:21       ` Phil Budne
  -- strict thread matches above, loose matches on Subject: below --
2021-09-17 20:18 Noel Chiappa
2021-09-17 20:47 ` Clem Cole
     [not found] <>
2021-09-17 14:09 ` Roland via TUHS
2021-09-17 14:33   ` Warner Losh
2021-09-17 15:32     ` Clem Cole
2021-09-17 16:04       ` Roland via TUHS
2021-09-17 16:14         ` Clem Cole
2021-09-17 16:44           ` Roland via TUHS
2021-09-17 16:13       ` Warner Losh
2021-09-17 16:17         ` Clem Cole
2021-09-17 16:05     ` Roland via TUHS

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