The Bell Laboratories relay computers were a series of computing machines built between 1939 and 1949. They were electromechanical, meaning that the actual computations were carried out by electrically-driven moving parts.

The Bell relay computers had their genesis in the mind of mathematician George Stibitz. In late 1937, while working for Bell Labs in New Jersey, Stibitz began researching the design of telephone relays (electrically powered switches). These relays had metal contacts that were opened and shut by a magnetic field generated by a current-bearing coil and were used to route, or "relay," telephone calls. When a relay was closed, an electrical signal (e.g., a telephone call) would be conducted through the closed metal contacts; when the relay was open, no signal could pass.

Stibitz was intrigued by the possibility of using relays to perform calculations. In particular, he noted that the on-and-off switching...