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

[Clem Cole via TUHS]

ITS was moved from the PDP-6 to a couple of different PDP-10
implementations. And TOPS-10 evolved from the DEC PDP-6 monitor. BBN wrote
Tenex for a modified PDP-10, but they had certainly learned many lessons
from their (modified) PDP-6  and PDP-1 systems

On Mon, Mar 23, 2026 at 9:15 PM George Michaelson via TUHS <tuhs at tuhs.org>
wrote:

> 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
> >
> >
>