Number 129 (Story #3), May 19, 1993 by Phillip F. Schewe and Ben Stein REVERSIBLE COMPUTATION AND REVERSIBLE LOGIC : in the computation process, energy is dissipated whenever information is destroyed. The lesson is: to dissipate less energy, don't discard information. One way to do this would be to build logic circuits that can run in reverse. That is, the circuits (and the computers using them) would return to their original states at the end of the computation cycle after having performed the required calculations. This idea has been promoted by Rolf Landauer and Charles Bennett of IBM, who spoke at the March APS Meeting in Seattle. In principle such circuits, performing reversible operations, would dissipate less energy than irreversible circuits (operating with no regard for the retention or destruction of information) performing irreversible operations. Ralph Merkle of Xerox said that the use of reversible circuitry, entailing also the use of reversible software, was not yet a priority for computer architects but would be early in the next century when the problems of heat dissipation (requiring large heat sinks) and energy consumption become more pressing. Already, Merkle said, computer systems account for 5% of all commercial electricity use in the U.S.; this might double by the turn of the century. (Dallas Morning News, 19 April 1993.)