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Questions tagged [pdp-7]

For questions about the DEC PDP-7 minicomputer.

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33 votes
2 answers
6k views

Why was UNIX never backported to the PDP-7?

Originally, UNIX was written in PDP-7 assembly, and then in PDP-11 assembly, but then when UNIX V4 began to be re-written in C in 1973 and was run mostly on the PDP-11. So far as I can tell, there ...
Omar and Lorraine's user avatar
18 votes
2 answers
3k views

What is the instruction set of the PDP-7?

The PDP-7 was a bookshelf-sized "minicomputer", with keyboard, magnetic and paper tape and printer I/O. According to Wikipedia, the first version of UNIX (then named Unics) was programmed in assembly ...
wizzwizz4's user avatar
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15 votes
2 answers
1k views

Null-terminated strings on the PDP-7?

I came across a post that states that Unix uses null-terminated strings, ASCIZ, because it was a feature of the PDP-7. This triggered my reading on the CIS instructions in the PDP-11, but these were ...
Maury Markowitz's user avatar
9 votes
2 answers
563 views

Why do the later 18 bit PDPs include both ones' and two's complement?

The PDP-1 is a ones' complement machine, and does some checks to make sure you (almost) never get negative zero. I'm struggling to think why anyone would want ones' complement arithmetic, but it was ...
Omar and Lorraine's user avatar
5 votes
2 answers
416 views

How to read/write word from DECtape on SIMH?

I am learning programming assembly for PDP-4 using SINH simulator. I stuck at understanding how tape drives work. I want to read one word from DECtape 550 unit 1 but I don't know how. I'm learning PDP ...
Codesynth's user avatar
4 votes
0 answers
286 views

What does this image in Space Travel represent?

I was touching up the Space Travel article on the Wiki and realized no one had answered a question I posted some time ago. I suspect someone here knows the answer. This image is used in the infobox to ...
Maury Markowitz's user avatar
3 votes
2 answers
365 views

Is it possible to get a pdp7 [closed]

Is it possible to get an original DEC pdp-7, if so how much would it be? I've looked around the internet, but I'm not finding anything.
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