Every digital computer needs a way to represent a binary digit, and the usual answers are switches: relays, tubes, or transistors. In 1954, Japanese researcher Eiichi Goto proposed something stranger: the parametron, a resonant circuit built from a ferrite core and a capacitor whose reactance is pumped at twice its resonant frequency.

The pumping makes the circuit oscillate at half the pump frequency, and — the clever part — there are two equally stable oscillation states, 180° apart in phase. Those two phases serve as binary 0 and 1. Logic is done not with voltage levels or current direction, but with the phase of an AC waveform.

To build a gate, several preceding parametrons are weakly coupled into the next stage. Because a parametron behaves like a regenerative amplifier, the small initial oscillation from the inputs grows to full amplitude, with same-phase signals reinforcing and opposite-phase signals cancelling. A three-input parametron is therefore inherently a majority gate. Tie one input permanently to 0 or 1 and it becomes AND or OR; reverse a coupling transformer's polarity and you get inversion. A chain of three parametrons can form an SR flip-flop, and Goto's 1959 paper shows more complex circuits such as a parity checker. Practical machines drove groups of parametrons with staggered clock phases so each stage settled before the next was excited.

Speed was the weakness. Even a fast parametron topped out around 6 MHz, and a computer built from them ran at clock frequencies near 140 kHz. On the plus side, each gate regenerates its output, so a single output could drive 10 to 20 inputs, and the components were cheap and reliable.

The technology powered a notable family of Japanese machines. The PC-1 ran at 15 kHz and added fixed-point numbers in 270 microseconds, using 4200 parametrons and 3 kW of power. The PC-2 (1960), commercialized as the FACOM 202, ran at 100 kHz with 9600 parametrons and drew 10 kW; the FACOM 212 used 8000 units at 5 kW. Other parametron machines included HIPAC-1, MUSASINO-1, NEAC-1101, and SENAC-1. The largest had 1,024 words of core memory, and parametrons could read magnetic cores without erasing them — unlike conventional core memory.

Active devices ultimately won on speed, and parametrons faded into history, though they saw side uses in numerical control of machine tools, a Morse-to-Teletype converter, and a prototype road sensor detecting passing cars. The Engineering and Technology History Wiki maintains a detailed collection on the technology and the machines that used it, and old papers on programming the PC-1 survive for the curious.