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Twistor memory is, similar to core memory, formed by wrapping magnetic tape around a current-carrying wire. It was developed at Bell Labs, but it was used for only a brief time in the marketplace between 1968 and the mid-1970s. It was often replaced by RAM chips.

Twistor memory used the same concept as core memory, but instead of small circular magnets, it used magnetic tape to store the patterns. The tape was wrapped around one set of the wires, say X, in such a way that it formed a 45 degree helix. The Y wires were replaced by solenoids wrapping a number of twisor wires. Selection of a particular bit was the same as in core, with one X and Y line being powered, generating a field at 45 degrees. The magentic tape was specifically selected to only allow magnetization along the length of the tape, so only a single point of the twistor would have the right direction of field to become magnetized.

Related Topics:
Magnetic tape
Magnetic core memory
DRAM
Bubble memory

References:
http://en.wikipedia.org/wiki/Twistor_memory