Early Digital Computers at Bell Telephone Laboratories

(Bell Labs) during the 20-some years following Bell Labs' entry into the digital computer era. In doing so, I describe various problems that Bell Labs was addressing and characteristics of the machines developed as solutions. During this period, Bell Labs was AT&T's research and development arm, and Western Electric was AT&T's manufacturing division. Western Electric and AT&T each owned 50 percent of Bell Labs, and AT&T owned 100 percent of Western Electric. The combination of AT&T, Western Electric, Bell Labs, and the telephone companies owned or controlled by AT&T was frequently referred to as the Bell System. In what follows I will not attempt to distinguish between the terms calculator and computer. For example, one could take the position that the Model I was a calculator and not a computer because of its lack of a stored program and other deficiencies depending on one's exact definition of computer. Also, I will not discuss Bell Labs' telephone call-switching machines. Model I Bell Labs' entry into the digital computer era occurred in 1937 when a research mathematician , George R. Stibitz, noticed similarities between circuit paths through electromagnetic relays (used by telephone companies for switching telephone calls) and the mathematical binary notation for numbers. To explore this thought over a weekend, Stibitz used some relays to build a binary adder. This adder would give, as output, the binary digits for the sum of two one-digit binary numbers that were input to the device. He called it the Model K, the K referring to his kitchen where he constructed it. Figure 1 shows a replica of the Model K that Stibitz, shown in Figure 2, constructed in 1991 for George Keremedjiev, director of the American Computer Museum. When Stibitz demonstrated the device to his management the following week, they were unimpressed that relays could perform binary arithmetic. However, in 1938, Stibitz was asked to design an electromechanical relay digital computer that could perform arithmetical calculations using complex numbers. Samuel B. Williams, a telephone system design engineer, was assigned to supervise its engineering and manufacturing. What had happened was that Stibitz's management had become aware that Bell Labs' computational staff was in an overload situation and felt that a Stibitz-designed relay machine could help alleviate the over-This article relates highlights from the digital computer development activities at Bell Telephone Laboratories for roughly the period 1937–1958. The history begins with a researcher using relays to …