What Was the Differential Analyzer?

David Senra, reading the book's account, says the differential analyzer was one of the world's first large-scale analog computers: a brain the size of a room, a metal calculus machine that could whir at a problem for days and nights before it stopped. Bush hired a young Claude Shannon to run it and put him in a room with a machine built to automate thought.

One problem, measuring the effects of the Earth's magnetic field on cosmic rays, took 30 weeks of spinning gears. When the work was done, the machine had solved by brute force equations so complex that attacking them with human brain power would have been pointless. Bush's lab then had the power to turn from the problems of industry to fundamental physics. It was the computer before the digital revolution, built to remove the art from math. In that work Shannon saw another way of automating thought, one far more powerful than the analog machine. Logic, just like a machine, was a tool for democratizing force. Built with enough precision and skill, it could multiply the power of the gifted and the average alike.

Less than a decade after Shannon's paper, the great analog machine was obsolete. Digital computers did the same work a thousand times faster, in real time, driven by thousands of logic gates. Their design was a direct descendant of Shannon's discovery.