read a bit. Reading uses the process of writing; the X and Y lines are powered in the same fashion that they would be to write a "0" to the selected core. If that core held a "1" at that time, a short pulse of electricity is induced into the sense/inhibit line. If no pulse is seen, the core held a "0". 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. The sense/inhibit line is shared by all of the cores in a particular plane, meaning that only one bit can be read (or written) at once. Core planes were typically stacked in order to store one bit of a word per plane, and a word could be read or written in a single operation by working all of the planes at once. Between reads or writes the data was stored magnetically. This means that core is a non-volatile memory. Manufacturing Manufacturing core was a major issue. The X and Y wires had to be threaded through the cores in a weave pattern, and the sense/inhibit line passed through every core in a plane. In spite of considerable effort, no one successfully automated the production of core, which remained a manual task into the 1970s. To increase memory density one had to use smaller cores, which greatly increased the difficulty of wiring them onto the lines. Although the density of core increased many times over its operational lifetime, the per-bit cost of core remained steady. Twistor An early iteration of the Twistor comprised a twisted ferromagnetic wire threaded through a series of concentric solenoids (see attached photo of a test rig for a single "bit"). The longer solenoid is the SENSE coil, the shorter one the WRITE coil. A single bit was written by pulsing the WRITE coil with a + (1) or - (0) current sufficient to magnetize the helical area beneath the coil in one of two directions. At one end of the stretched wire was the READ solenoid - when pulsed it sent an acoustic wave through the wire. As the acoustic pulse passed under each SENSE coil it induced a small electrical pulse, either + or - depending on the direction of magnetization of the region of the wire. Thus with each pulse a "byte" could be read