Pilot ACE

The Pilot ACE was one of the first computers built in the United Kingdom at the National Physical Laboratory (NPL) in the early 1950s. It was also one of the earliest stored-program computers, joining other UK designs like the Manchester Mark 1 and EDSAC of the same era. The design is one of the earliest general computers designed by Alan Turing, although he left NPL before it was completed.

Pilot ACE was a preliminary version of the full ACE, which had been designed by Alan Turing. After Turing left NPL (in part because he was disillusioned by the lack of progress on building the ACE), James H. Wilkinson took over the project. Donald Davies, Harry Huskey and Mike Woodger were involved with the design. The Pilot ACE ran its first program on 10 May 1950, and was demonstrated to the press in December 1950.

Although originally intended as a prototype, it became clear that the machine was a potentially useful resource, especially given the lack of other computing devices at the time. After some upgrades to make operational use practical, it went into service in late 1951, and saw considerable operational service over the next several years. One reason the ACE was useful is that it was able to perform floating point arithmetic necessary for scientific calculations. Wilkinson tells the story of how this came to be.

The Pilot ACE was built without hardware for multiplication or long division, in contrast to other computers at that time. The ACE started out using fixed-point multiplication and division implemented as software. It soon became apparent that fixed point arithmetic was a bad idea because the numbers quickly went out of range. It only took a short time to write new software so that the ACE could do floating-point arithmetic. After that, James H. Wilkinson became an expert and wrote a book on rounding errors in floating-point calculations, which eventually sold well.

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