
The PDP-7 Where Unix Began - stargrave
https://bsdimp.blogspot.com/2019/07/the-pdp-7-where-unix-began.html
======
Torwald
> By porting Unix to the PDP-11 in 1970, the group ensured Unix would live on
> into the future.

I have a question about that. Why would they do this?

What was so valuable in these few lines of (mostly proprietary) code, that you
would make the effort to port instead of just writing from scratch on the new
machine?

If you take a look at what came later, a lot of much more substantial software
packages were made by a single bedroom coder in his spare time.

Why port? It couldn't be to save effort? (At least the conceptual level of
things would remain the same if you start from scratch.)

~~~
Merrill
About 1970 the first minicomputers were being applied to operations,
administration and maintenance functions in the Bell System. The PDP-7 was too
expensive and the PDP-8 was too limited to compete favorably with others. The
PDP-11 was applied widely and if the Unix OS was to be used by the development
groups instead of the DEC operating systems, it had to be ported.

~~~
ncmncm
The port wasn't motivated by the development groups. It was sold to management
as a word processing / typesetting system.

I vividly remember my first encounter with Unix, in an ACM journal archive at
the local university library as a teenager in the late '70s, utterly
astonished to find _lower-case_ computer commands and prompts.

~~~
Merrill
True, the development groups weren't too keen on Unix. They wanted to choose
the minicomputer and operating system from those commercially available and
get on with developing applications without the risks and effort of using an
unproven operating system. But Research always wanted to demonstrate that they
were contributing to the company, so eventually Unix had to be adopted.

Use by development groups for Western Electric products was different from the
in-house Unix systems run by the Bell Labs data center that were used as time
shared systems for email, general computing, and document production using
nroff and memo macros. Moving away from all upper case made line printers less
efficient, but about that time laser phototypesetting became available.

~~~
ncmncm
The main thing at the time was that mixed-case Teletypes were becoming common.

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peter303
Note CRTs where a luxury item in the early 1970s. A 5x7x64 character generator
requires 2240 bits uncompressed. Perhaps get closer to 1K if you had some run
length compression. In my 1975 MIT digital lab the 1K memory chips where kept
locked up because they were the most expensive chips at that time. By 1977 a
lab I worked in bought a CRT terminal for each student because character ROMs
had dropped in price.

~~~
aap_
The characters are not actually stored as rasters though. There are
up,down,left,right,intensify and end signals that control the beam and the
logic and no more than 30 pulses per character. In fact, I took photos of the
"ROM" earlier this year:
[https://imgur.com/a/QnFFkg6](https://imgur.com/a/QnFFkg6)

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bsdimp
[https://bsdimp.blogspot.com/2019/10/video-footage-of-
first-p...](https://bsdimp.blogspot.com/2019/10/video-footage-of-first-
pdp-7-to-run-unix.html) has some further speculation... Footage of the PDP-7
that ken would later use to create Unix.

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tempodox
> V0 Unix could run on only one of the PDP-7s.

Wow, I wonder how the history of UNIX would have panned out if that machine
hadn't happened to land at Bell Labs.

~~~
pmiller2
I can’t really speculate on that, but I can say the PDP series is a dream to
program. The instruction set is simple and orthogonal, and you can hold an
accurate model of the whole machine in your head that tells you exactly, step
by step, what will happen when your program is executed. I don’t know if any
other contemporary machines also had these properties, but I do think it makes
it an ideal research machine for creating a new programming environment (and
that’s really what UNIX was initially). That makes me think it was very likely
either the PDP or a similar machine would end up at Bell Labs for people to
develop on.

~~~
AtlasBarfed
I think I learned -7 or -8 assembly in my comp org class. It had about 8
instructions and you had to make your own division instruction, and I think
multiplication.

Then we moved onto a bit of 680x0. Yeah, that was different.

A simulator for it was pretty easy to write, switches and all.

~~~
pmiller2
I learned on a PDP-11, but we had 8’s available, too. They felt very similar.
I think the 11 had maybe 15-ish instructions?

Edit: just checked, and the 11 has about 70 instructions. I think MACRO-11
might abstract over many of them, making it look like it has fewer
instructions. The instructions group nicely into a few families, which makes
things really easy.

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peter_d_sherman
Amazing that the Unix of that day ran on an 8KB (not MB, not GB), 8KB machine
with just 1MB (not GB, not TB), much-slower than today's SSD's, disk.

Compare that to Linux, its most popular descendant Unix of today...

Today's Linux requires a tad more memory and disk than that... just a _tad_...
<g>

~~~
ncmncm
Note that wasn't the Unix we think of when we talk about Unix. It was written
in assembly code. C didn't properly exist yet.

