Who was Donald Davies?

Donald Davies was a computer scientist who worked at the National Physical Laboratory (NPL). He started working there in 1947 with Alan Turing, who led the design of the Automatic Computing Engine (ACE) computer. This project turned out to be overambtious and was taken over by Donald Davies, who delivered a less amibitious Pilot ACE computer in 1950.

One of Donald Davies' most remarkable achievements is that of Packet Switching. He came up with this idea in 1965 while working at NPL. It is a method of grouping data into packets for transmision over a digital network, and is used today in the internet.

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In 1947, Donald Davies asked Alan Turing about some problematic details that he found with his Universal Turing Machine as he described it in his famous paper On Computable Numbers with an Application to the Entscheidungsproblem. Turing became very irritated with Davies, and told him that he was wasting the time of both of them.

This narrative is retold very nicely in the book The Essential Turing (Oxford University Press, 2013) by Jack Copeland on pages 92-93. This book also includes, on pages 103-124, Davies' article Corrections to Turing's Universal Computing Machine, as well as Turing's famous paper On Computable Numbers with an Application to the Entscheidungsproblem on pages 58-90, and many other stories and articles pertaining to Alan Turing.

Donald Davies may very well have found the very first computer bugs in the world, although Alan Turing probably never intended for his Universal Turing Machine to run on an actual computer.