Lecture on the Automatic Computing Engine (1947)

Abstract

On 8 December 1943 the world’s first large-scale special-purpose electronic digital computer—‘Colossus’, as it became known—went into operation at the Government Code and Cypher School (see ‘Computable Numbers: A Guide’, ‘Enigma’, and the introduction to Chapter 4). Colossus was built by Thomas H. Flowers and his team of engineers at the Post Office Research Station in Doll is Hill, London. Until relatively recently, few had any idea that electronic digital computation was used successfully during the Second World War, since those who built and worked with Colossus were prohibited by the Official Secrets Act from sharing their knowledge. Colossus contained approximately the same number of electronic valves (vacuum tubes) as von Neumann’s IAS computer, built at the Princeton Institute of Advanced Study and dedicated in 1952. The IAS computer was forerunner of the IBM 701, the company’s first mass-produced stored-programme electronic computer (1953). The first Colossus had 1,600 electronic valves and Colossus II, installed in mid-1944, 2,400, while the IAS computer had 2,600. Colossus lacked two important features of modern computers. First, it had no internally stored programmes (see ‘Computable Numbers: A Guide’). To set up Colossus for a new task, the operators had to alter the machine’s physical wiring, using plugs and switches. Second, Colossus was not a general-purpose machine, being designed for a specific cryptanalytic task (involving only logical operations and counting). Nevertheless, Flowers had established decisively and for the first time that large-scale electronic computing machinery was practicable. The implication of Flowers’s racks of electronic equipment would have been obvious to Turing. Once Turing had seen Colossus it was, Flowers said, just a matter of Turing’s waiting to see what opportunity might arise to put the idea of his universal computing machine into practice. Precisely such an opportunity fell into Turing’s lap in 1945, when John Womersley invited him to join the Mathematics Division of the National Physical Laboratory (NPL) at Teddington in London, in order to design and develop an electronic stored-programme digital computer—a concrete form of the universal Turing machine of 1936.