Twistor memory

Both forms were able to be manufactured using automated processes, which was expected to lead to much lower production costs than core-based systems.

The basic ideas behind twistor also led to the development of bubble memory, although this had a similarly short commercial lifespan.

This is accomplished by powering a selected X and Y wire both to the current level that will, by itself, create ½ the critical magnetic field.

If that core held a "1" at that time, then the magnetic state flips to a "0" and the transition causes a short pulse of electricity to be induced into the sense/inhibit line.

This process is destructive; if the core did hold a "1", that pattern is destroyed during the read, and has to be re-set in a subsequent operation.

In spite of considerable effort, no one successfully automated the production of core,[citation needed] which remained a manual task into the 1970s.

An early iteration of the Twistor comprised a twisted ferromagnetic wire threaded through a series of concentric solenoids.

The original twistor system used permalloy tape wrapped around a 3 mil copper wire.

Although the folding process that completed the twistor might be carried out by hand, the layup and laminating of the sheets was easily handled by machine.

Improved versions of twistor also wrapped the section of bare copper initially used solely for the return path, thereby doubling density without any changes to the production techniques.

Instead, it used a larger current in the solenoid, large enough to flip all of the bits in that loop, and then used the twistor wires as the read line.

To do this, one-half of each solenoid loop was replaced with an aluminum card into which tiny vicalloy bar magnets were embedded.

The resulting field was greater than the write strength, causing the permalloy state to flip.

If the bit was beside an unmagnetized bar magnet in the card, the field was not opposed and the flip caused a current pulse in the twistor wire, reading a "1".

The permanent magnet twistor (PMT) was re-programmed by removing the plates and placing them over a custom writer.

This tape was coated with coballoy instead of permalloy, which is much "harder" magnetically, requiring about twice the field in order to flip.

Writes were slightly more complex, due to the fact that piggyback twistors all featured the magnetic tape along the entire length of the X wire.

Much of the development funding was supplied by the US Air Force, as twistor was to be used as the main memory in the LIM-49 Nike Zeus project.

By 2017 all remaining TSPS and ESS installations used to provide telephone service in rural areas of the United States had been removed.