No. 27:
Vannevar Bush's Differential

Today, we meet the grandest computer of the early 1940s. The University of Houston's College of Engineering presents this series about the machines that make our civilization run, and the people whose ingenuity created them.

We tend to view the computer as having come into being only during the past 30 years. No doubt, it has come into its own during that period. But serious attempts to do complicated machine calculations were under way well before WW-II.

The most important pre-war effort was started in the 1920s by Vannevar Bush. It culminated in 1942 with the dedication of his huge Rockefeller Differential Analyzer at MIT -- a one-hundred-ton machine with 2000 vacuum tubes and 150 motors.

Bush's Analyzer was an analog computer. An analog computer actually carries out an analogy of a real physical process -- in this case, a mixed electrical-mechanical analogy. A digital computer is quite different. It breaks all computations down into sequences of additions and subtractions and solves equations by doing a lot of simple arithmetic.

Bush's computer quickly fell under the pall of WW-II secrecy, but only after the head of Electrical Engineering at MIT had proclaimed that it would "mark the beginning of a new era in mechanized calculus," and MIT president Compton had announced that it would be "one of the great scientific instruments of modern times."

When this wonderful device emerged from secrecy five years later, it turned out that it'd slipped into obsolescence. The new breed of high-speed digital computers simply overtook it.

Historian Larry Owens looks at this fall from grace and asks sadly, "How does one tell the story of a machine?" Owens concludes that the real importance of the fall is that it so clearly illustrates a change in the very character of engineering after the war. Bush, he observes, represented a kind of engineering that was in contact with the workshop. His computer was made up of complex mechanical and electrical elements. It thought the way prewar engineers thought -- in physical, graphical terms. The modern digital computer, he points out, speaks in a mathematical language to the more abstract and mathematical breed of postwar engineers.

I'm John Lienhard, at the University of Houston, where we're interested in the way inventive minds work.

(Theme music)

Owens, L. Vannevar Bush and the Differential Analyzer: The Text and Context of an Early Computer. Technology and Culture, Vol. 27, No. 1, January 1986, pp. 63-95.

For more on Vannevar Bush, see Episode 685.

This episode has been revised and expanded as Episode 1319.