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 and programmed by the MIT Instrumentation Lab and built by Raytheon.
Contrary to ordinary coincident-current magnetic core memory, which was used for RAM at the time, the ferrite cores in a core rope are just used as transformers. The signal from a word line wire passing through a given core is coupled to the bit line wire and interpreted as a binary "one" while a word line wire that bypasses the core is not coupled to the bit line wire and is read as a "zero". In the AGC, up to 64 wires could be passed through a single core.
Software written by MIT programmers was woven into core rope memory by female workers in factories. Some programmers nicknamed the finished product LOL memory, for Little Old Lady memory.[1]
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A relatively large (by the standards of the time) amount of data could be stored in a small installed volume of core rope memory (72 kilobytes per cubic foot; roughly 2.5 megabytes per cubic meter); about 18-folda the amount of data per volume compared to standard read-write core memory.
| Memory technology |
Data units per cubic foot | Data units per cubic meter | ||
|---|---|---|---|---|
| Bytes | Bits | Bytes | Bits | |
| Core rope ROM | 72 KB | 576 Kbit | ~2.5 MB | ~20 Mbit |
| Magnetic core RAM | 4 KB | 32 Kbit | ~140 KB | ~1 Mbit |
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