July 2001

Claude Shannon: Reluctant Father of the Digital Age

Continued from page 1

By M. Mitchell Waldrop

Tinkering toward Tomorrow

For Shannon, it was all just another way to have fun. "Claude loved to laugh, and to dream up things that were offbeat," says retired Bell Labs mathematician David Slepian, who was a collaborator of Shannon's in the 1950s. Shannon went at math like a stage magician practicing his sleight of hand: "He would circle around and attack the problem from a direction you never would have thought of," says Slepian-only to astonish you with an answer that had been right in front of your face all the time. But then, Shannon also had a large repertoire of real card tricks. He taught himself to ride a unicycle and became famous for riding it down the Bell Labs hallways at night-while juggling. ("He had been a gymnast in college, so he was better at it than you might have thought," says his wife Betty, who gave him the cycle as a Christmas present in 1949.)

At home, Shannon spent his spare time building all manner of bizarre machines. There was the Throbac (THrifty ROman-numerical BAckward-looking Computer), a calculator that did arithmetic with Roman numerals. There was Theseus, a life-sized mechanical mouse that could find its way through a maze. And perhaps most famously, there was the "Ultimate Machine"- a box with a large switch on the side. Turn the switch on, and the lid would slowly rise, revealing a mechanical hand that would reach down, turn the switch off, and withdraw-leaving the box just as it was.

"I was always interested in building things with funny motions," Shannon explained in a 1987 interview with Omni magazine (one of the few times he spoke about his life publicly). In his northern Michigan hometown of Gaylord, he recalled, he spent his early years putting together model planes, radio circuits, a radio-controlled model boat and even a telegraph system. And when he entered the University of Michigan in 1932, he had no hesitation about majoring in electrical engineering.

After graduating in 1936, Shannon went directly to MIT to take up a work-study position he had seen advertised on a postcard tacked to a campus bulletin board. He was to spend half his time pursuing a master's degree in electrical engineering and the other half working as a laboratory assistant for computer pioneer Vannevar Bush, MIT's vice president and dean of engineering. Bush gave Shannon responsibility for the Differential Analyzer, an elaborate system of gears, pulleys and rods that took up most of a large room-and that was arguably the mightiest computing machine on the planet at the time (see "Computing After Silicon," TR May/June 2000).

Conceived by Bush and his students in the late 1920s, and completed in 1931, the Differential Analyzer was an analog computer. It didn't represent mathematical variables with ones and zeroes, as digital computers do, but by a continuous range of values: the physical rotation of the rods. Shannon's job was to help visiting scientists "program" their problems on the analyzer by rearranging the mechanical linkages between the rods so that their motions would correspond to the appropriate mathematical equations.

Shannon couldn't have asked for a job more suited to his love of funny motions. He was especially drawn to the analyzer's wonderfully complicated control circuit, which consisted of about a hundred "relays"-switches that could be automatically opened and closed by an electromagnet. But what particularly intrigued him was how closely the relays' operation resembled the workings of symbolic logic, a subject he had just studied during his senior year at Michigan. Each switch was either closed or open-a choice that corresponded
exactly to the binary choice in logic, where a statement was either true or false. Moreover, Shannon quickly realized that switches combined in circuits could carry out standard operations of symbolic logic. The analogy apparently had never been recognized before. So Shannon made it the subject of his master's thesis, and spent most of 1937 working out the implications. He later told an interviewer that he "had more fun doing that than anything else in my life."