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

[John Levine via TUHS]

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