The Core rope memory reference article from the English Wikipedia on 24-Apr-2004 (provided by Fixed Reference: snapshots of Wikipedia from wikipedia.org)

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, allowing it to store four 16-bit words of data, while the data density of magnetic core RAM was one bit per core. A two-bit code selected which of the four words to be read from a particular core in the rope.

See also: computer storage

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