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Core rope memory
Core rope memory is a form of read-only memory (ROM) for computers, first used by early NASA Mars probes and then in the Apollo Guidance Computer (AGC) designed by MIT and built by Raytheon.
Contrary to ordinary magnetic core memory, which was used for RAM at the time, all the ferrite cores in a core rope are permanently magnetized in one direction. The signal from a wire passing through a given core is interpreted as a binary "one" while a wire that bypasses the core is read as a "zero". In the AGC, up to 64 wires could be passed through a single core. A relatively large amount of data could be stored in a small volume; the capacity of one cubic foot of it was 36,864 sixteen bit words (compared to only 2048 sixteen bit words of standard read-write core memory in a similar volume).
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