Dr. Claude Elwood Shannon, who developed the theory that drives all modern computers, died last month at 84.

Shannon’s master’s thesis, one of the most influential ever written, showed how Boolean logic could be carried out with electrical switching circuits. Boolean logic represents and solves problems by manipulating just two symbols, 1 and 0. The symbol 1 could be represented by a switch turned on, and 0 by a switch turned off. Each of these switches was one "bit," possibly the first published occurrence of the word.

By adding enough extra bits, he theorized, a message could be sent without error through a noisy tunnel. This work has developed over time into the sophisticated error-correction protocols now used in computers.

As a boy, his best subjects in school in Gaylord, Michigan, where his mother was principal of the high school, were science and mathematics. At home he built model planes and boats, and a telegraph system to a friend’s home a half mile away. His childhood hero was Thomas Edison, who he later discovered was a distant cousin.

Shannon got a bachelor’s degree in mathematics and electrical engineering from the University of Michigan in 1936. He got a master’s in electrical engineering and a Ph.D. in mathematics from M.I.T. in 1940, where he worked as a research assistant with Dr. Vannevar Bush on the Bush differential analyzer, the most advanced calculating machine of its time.

A complex relay circuit that controlled the differential analyzer caught his attention, and led him to focus on relays and switching circuits as a way to represent two-valued systems, like Boolean logic.

But his thesis was largely motivated by the telephone industry’s need for a mathematical language that could describe the behavior of switching circuits.

Shannon realized very early that ones and zeros could represent far more than numbers: they could be words, sounds, images, even ideas. It was the separation of the message from the medium that carried it that was ultimately one of his most important contributions.

After graduating from M.I.T., Shannon took a job at Bell Laboratories, where he continued to work on switching circuits, information theory, and efficient communications systems.

In 1948 he published "A Mathematical Theory of Communication" in the Bell System Technical Journal, which demonstrated that all information sources—telegraph keys, people speaking, television cameras, etc.—have a "source rate" which can be measured in bits per second. Communication channels have a "capacity" measured by the same means. The channel can carry the information only if the source rate does not exceed the capacity.

"Few other works of this century have had greater impact on science and engineering. By this landmark paper and his several subsequent papers on information theory he has altered most profoundly all aspects of communication theory and practice,'' said Professor Irving Reed at the 1981 International Symposium on Information Theory.

Most computerized chess-playing systems are based on his 1950 paper, "Programming a Computer for Playing Chess."

Shannon ideas have made a tremendous impact on the shaping of modern society, but he was known among his family and associates for a sense of humor. His home was filled with amusing devices, like THROBAC (THrifty ROman numeric BAckward looking Computer), a calculator that performs its arithmetical functions in the Roman number system.

He also built "The Ultimate Machine," described by Archur C. Clarke in Voice Across the Sea. It was a box with a switch. When thrown, the box buzzes, the lid opens, and a hand emerges, turning off the switch, and the lid then closes.

His work on the chess programs and a maze-solving mouse helped create the field of artificial intelligence.

"The image of that great stream of ideas still persists in everyone his mind ever touched," said Dr. Marvin Minsky, who worked with Shannon at M.I.T.