[TUHS] porting to different systems, Bootstrapping UNIX - how was it done

[George Michaelson via TUHS]

EMAS was ported from the ICL 1900 to the 2900 at Edinburgh Uni across this
time.  In like sense TOPS-10 was ported from the 10 to the 20 but that was
at worst a marginal conversion. Obviously the entire suite of DEC RSTS type
operating systems were cross ported to the variants of the PDP11 on an
as-emerged basis, but I suspect like tops10/20 that was hardly a "port" in
any real sense

but I believe the 1900 an 2900 were quite different, the 1900 was 24bit
word, 6bit byte. the 2900 32 bit word 8bit byte. (I was a kid at the time
of course, I'm not a dinosoar like the rest of you) -so I think it was more
than just uplift.  Different code/microcode.

-G

On Tue, Mar 24, 2026 at 10:57 AM John Levine via TUHS <tuhs at tuhs.org> wrote:

> According to Noel Chiappa via TUHS <jnc at mercury.lcs.mit.edu>:
> >2 - Move a set of existing software from one type of machine to another.
> (A
> >much more common event, now that we have portable software. Speaking of
> >portable software, I'm still amazed that this, which became one of Unix's
> >most important attributes, and a major driver in its spread, after V7,
> does
> >not appear to have been really thought about before V6/V7 was ported to
> >several other architectures.)
>
> I don't think it occurred to anyone until that that it would even make
> sense to
> move an operating system from one kind of computer to another.
> Historically,
> architectures were different, data formats were different, I/O
> architecture was
> different, and everything was written in assembler or maybe a language
> tied to
> the system like Burroughs Algol.
>
> By a decade after S/360 came out, computer architectures had all converged
> on
> 8-bit byte addressable two's complement designs with multiple registers.
> (Older
> machines like the PDP-10 weren't dead yet but it was just a matter of
> time.)
> Then Unix came along, written mostly in C which was highly portable to
> those
> 8-bit byte addressable machines. The group at the Labsy allegedly picked
> the
> Perkin Elmer 7/32 because it was as different as possible from the PDP-11,
> but
> it wasn't all that different. It was 32 bits but the data formats were the
> same
> (give or take a few details of floating point), addressing and memory
> protection
> were similar to the PDP-11, and it had terminals and disks.
>
> Wollongong and the Labs separately did 7/32 ports, both probably observing
> that if they retargeted the C compiler to the 7/32 and recompiled the
> PDP-11
> C code, they were about 80% of the way there, so the rest of the work was
> a manageable project.
>
> R's,
> John
> --
> Regards,
> John Levine, johnl at taugh.com, Primary Perpetrator of "The Internet for
> Dummies",
> Please consider the environment before reading this e-mail. https://jl.ly
>
>