Transformer read-only storage

Transformer read-only storage (TROS) was a type of read-only memory (ROM) used between the mid-1940s to the late 1960s, prior to the common use of semiconductor ROM. TROS consisted of wires fed through and around transformer cores. The wires would register binary digits (1s and 0s) through inductance and separate wires sensing the change in current.

Transformer read-only storages were first invented by T. L. Dimond in 1945 at Bell Laboratories for the No. 5 Crossbar switch to assist in the automatic message accounting (AMA) equipment. Later applications include the Bell Laboratories Model 6 computer and the IBM System/360 Model 20 and Model 40. TROS was considered simple in design, albeit with flaws that discouraged later applications due to demands for higher computer performance.