Pilot ACE

In February 1946 Turing submitted a design report to the National Physical Laboratory for the Automatic Computing Engine. It was considerably more detailed than von Neumann's EDVAC draft: circuits, instruction formats, even a cost estimate. The bureaucracy proved slower than the machine would be, Turing left for Manchester in 1948, and James Wilkinson, Donald Davies and Harry Huskey instead built a simplified test version that first ran on 10 May 1950.

The design lacked most of what later became standard. Arithmetic was largely performed by shuttling numbers between delay lines rather than through a single arithmetic unit, and every instruction stated explicitly where the next one lived. The programmer had to place code so that the delay line happened to present the right word at the right moment — optimum coding, which made Pilot ACE unusually fast for its day and unusually painful to write for. English Electric sold the commercial derivative, DEUCE, in some thirty-odd copies. Davies went on to invent packet switching.