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Questions tagged [pdp-8]

For questions regarding the DEC PDP-8 minicomputer.

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27 votes
4 answers
4k views

Use of undocumented opcodes

I figure this is fitting for Retrocomputing.SE because CPUs like the 6502 and Z80 and the PDP-8, and probably others, have undocumented instructions and will happily execute them, in contrast with ...
Omar and Lorraine's user avatar
20 votes
5 answers
3k views

Size of the PDP-8

What is the physical size of a PDP-8? The photographs I found seem to be evenly divided between showing it as a compact unit that looks maybe one foot high, and as a tall cabinet maybe five or six ...
rwallace's user avatar
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14 votes
3 answers
2k views

How did the PDP-8 handle strings?

The PDP-8 was a popular 12-bit minicomputer of the late sixties. It used word addressing, so that it always dealt in 12-bit words, of which it could address 4096 with a full bank of core memory. In ...
rwallace's user avatar
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8 votes
3 answers
1k views

Arithmetic operations on multiple words on the PDP-8

For the PDP-8 with its strange ISA, I've always wondered what the "standard" (i.e. fastest) way to do arithmetic operations (add, subtract, maybe multiply) on integers consisting of multiple words was....
dirkt's user avatar
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16 votes
4 answers
3k views

PDP-8 transistor count

https://en.wikipedia.org/wiki/Transistor_count provides some transistor count figures for early microprocessors, e.g. 8008 and 6502 both listed at around 3500. The PDP-8 was a 12-bit computer with a ...
rwallace's user avatar
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15 votes
3 answers
1k views

Conditional skip instructions of the PDP-8

I am interested in the SKIP instructions on the PDP-8. These test the accumulator and Link bit, and they skip the next instruction if the condition holds. The instructions are: OR GROUP SMA - Skip ...
Omar and Lorraine's user avatar
9 votes
1 answer
547 views

PDP-8 conditional skip and 2-word instructions

PDP-8 heavily relied on conditional skips: instructions that under some circumstances would skip the following instruction. Among them are, for example: ISZ SZA/SNA/etc. group of instructions many IO ...
lvd's user avatar
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