Complex Number Calculator

George Stibitz created the Complex Number Calculator (CNC) at Bell Labs in 1937. Called the Model K, it was capable of calculating complex numbers using binary addition, subtraction, multiplication, and division. It was entirely relay-based and was based on Stibitz’s theory that the electromechanical relays of telephone switching systems could be used for other things. It was built using flashlight bulbs and a switch made from a tobacco tin. The brain consisted of 450 telephone releays and 10 crossbar switches. It was capable of producing two eight place complex number equations in about thirty seconds, and ran with three teletypewriters.

Bell commissioned a research program in 1938, and it was officially completed on January 8th, 1940. It was demonstrated to the American Mathematical Society at Dartmouth on Sept.11th, 1940 and became the first computer to be used remotely over a telephone line when Stibitz sent it commands at Bell Labs in New York City. The device was one of many that provided the foundation for digital computers. It was later renamed the Model 1 Relay Computer and operated until 1949.

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