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Twistor memory is a type of computer memory that predated modern-day RAM and was eventually replaced by it. Twistor memory is similar to core memory. It is formed by wrapping magnetic tape around a current-carrying wire. It uses the magnetic tape to store patterns. A variant of twistor memory called piggyback twistor can also be used as ROM. Twistor memory was introduced in 1957 and used through the mid-1970s.
Twistor memory is a type of magnetic memory that was invented by Andrew Bobeck at Bell Labs in 1957. Twistor memory was similar to core memory, and was an improvement over the previously used circular magnets. Twistor memory uses magnetic tape to store patterns; the tape is wrapped around current-carrying wires.
Twistor memory is constructed by threading the core magnets with two crossed wires, X and Y. The construction comprised of the magnets and wires forms a matrix called the plane. A magnetic field is created as the core magnets sit on the wires at a 45-degree angle. Both reading and writing operations are accomplished with the help of a third wire called the inhibit line.
The writing operation of twistor memory is done by selecting both the X and Y wire, such that the current level creates a ½ critical magnetic field. This causes a difference in the field at the crossing point to become greater than the saturation point of the core. Thus, the core stores bits by picking up the external field and the ones and zeros are represented based on the direction of the flow of current.
The reading operations also make use of the process of writing. A pattern is destroyed during the read and has to be reset in the following operation. Only one bit can be read or written at once.
Although twistor memory was primarily used as core memory, it can also be used to make ROM memory. A variant of twistor memory with reprogrammable features was known as piggyback twistor. Another variant named twistor uses solenoids and the tape is wound around one set of wires in a 45-degree helix.
The introduction of semiconductor memory ended the use of twistor memory. The bubble memory invented in the 1980s uses a similar concept.