The highly productive habits of Alan Turing

June 23 marks the 100th birthday of Alan Turing. If I had to name five people whose personal efforts led to the defeat of Nazi Germany, the English mathematician would surely be on my list. Turing's genius played a key role in helping the Allies win the Battle of the Atlantic—a naval blockade against the Third Reich that depended for success on the cracking and re-cracking of Germany's Enigma cipher. That single espionage victory gave the United States control of the Atlantic shipping lanes, eventually setting the stage for the 1944 invasion of Normandy.

But even before this history-changing achievement, Turing laid the groundwork for the world we live in today by positing a "universal computing machine" in 1936. "It is possible to invent a single machine which can be used to compute any computable sequence," he contended. His proposed device could read, write, remember, and erase symbols. It would produce the same results "independent of whether the instructions are executed by tennis balls or electrons," the historian George Dyson notes, "and whether the memory is stored in semiconductors or on paper tape."

Turing's essential idea, aptly summarized by his centenary biographer Andrew Hodges, was "one machine, for all possible tasks." The concept guided the generation of computer theorists and builders who flourished after the Second World War, among them Turing himself for a time.