jan 21, 1964 - Transformer Read-Only Storage (TROS)

Description:

IBM introduces Transformer Read Only Storage (TROS) with the arrival of the IBM 360. TROS modules preceded solid-state ROM chips, and each bit of this read-only memory for microcode was a little magnetic transformer. Punches in the mylar strips controlled whether current flowed through the transformer or around it, representing a binary zero or a one.