[coder543]

In the context of this thread, I believe even a digital computer would have to be rebuilt if the program is wrong... :P

Unless you typically salvage digital computers from the wreckage of a failed rocket test and stick it in the next prototype. If the FCC is wrong, kaboom.

[Tommstein]

Presumably they meant a program being discovered to be wrong before the computer was actually launched. And meant literally building a whole new computer, not just recompiling a program.

[KMag]

For the Apollo Guidance Computer, changing the program meant manually re-weaving wires through or around tiny magnet rings. A good part of the cost of the computer was the time spent painstakingly weaving the wires to store the program.

[neodypsis]

There's a very nice video about the assembly lines MIT made just for building the Apollo computer [0].

0. https://www.youtube.com/watch?v=ndvmFlg1WmE

[denton-scratch]

Pardon me, but why would you have to re-weave wires around magnetic rings? The magnetic rings are for storing data; the whole point is that you can change the data without rewiring the memory. If you have to re-wire permanent storage (e.g. program storage), that's equivalent to creating a mask ROM, which is basically just two funny-shaped sheets of conductor. There's no need for magnetic rings.

[KMag]

No, I'm not talking about magnetic core memory. Core rope memory also used little magnetic rings.

https://en.wikipedia.org/wiki/Core_rope_memory input wires were energized, and they were coupled (or not) to the output wires depending on if they shared a magnetic ring (or not).

[denton-scratch]

Thanks! I'd never heard of rope memory.

[garaetjjte]

https://www.youtube.com/watch?v=hckwxq8rnr0

[hinkley]

Because it’s not RAM, it’s ROM.

[Anarch157a]

Only if the bug was caught after the computer had been assembled for the mission. For development, they used a simulator. Basically, a cable connected to a mainframe, with the bigger computer simulating the signals a bundle of core rope would produce.

[hinkley]

Yeah, though to be fair, some of the programs Apollo ran were on hand woven ROMs, so I may be making too fine a distinction. The program itself was built, not compiled. It if we are comparing with today, it would just be installed, not constructed.

[nothercastle]

I had assumed it meant more simple things like balanced balancing pneumatic or mechanical components that always put you at the the correct ratio sort of like a carburetor vs fuel injection.

[scaredginger]

I'm pretty sure you can perform tests and find defects without actually flying the rocket