Build Your Own NASA Apollo Landing Computer

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32 points·alexyes··3 comments

"It was the first computer to use integrated circuits (ICs), running at 1 Mhz it offered four 16-bit registers, 4K words of RAM and 32K words of ROM. The AGC mutlitasking operating system was called the EXEC, it was capable of executing up to 8 jobs at a time."

And it ran in a little metal can we sent to the moon in the 1960s. Wow.

There are lots of amazing stories about the AGC:

- It has a mysterious intruction named EDRUPT ("Ed's interrupt") that took several years to be reverse engineered afterwards.

- The 32k ROM was stored on rope memory: bundles of wires with a ferrite core assembled by hand in factories.

EDRUPT does the following:

* Inhibits interrupts until the next RESUME instruction (as if a hardware interrupt had been encountered).

* Loads the Z register into the ZRUPT register. (Incidentally, so far I've seen only a single instance of this instruction, in Luminary 131, and the return address is never used.)

* Takes the next instruction from address 0 (which presumably has been pre-loaded with "TC something").

The instruction also shoves a couple of register values onto the data bus, but does not save them into memory. My assumption is that some kind of external instrumentation was able to capture these values, but that they were irrelevant to normal execution.

Source: http://www.ibiblio.org/apollo/assembly_language_manual.html

Supposedly it was mainly used for self-testing.

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