Computers consume some 5% of the commercial energy used in the U.S., according to the Environmental Protection Agency. That costs plenty. And as computer chips become denser, the electricity surging through their circuits makes them harder and harder to keep cool. Now, some scientists are proposing that an unusual theoretical design called "reversible computing" may help. After performing a calculation, a reversible computer would return to its initial state by running the calculation backward and recovering the charges stored in its capacitors instead of discharging them as excess heat.
The concept has been around since the early 1970s, but mainly as an academic exercise. In the past couple of years, a few researchers have begun working on designs that could start producing real reversible-logic chips. One enthusiast is Ralph Merkle, a researcher at Xerox Corp.'s Palo Alto Research Center, who believes such machines can be built from today's most common low-power chips. Within a few years, says Merkle, reversible logic chips could be used in exotic applications such as computers in space, where energy consumption is critical. Predicts Merkle: "Sometime in the next century, reversible logic will dominate computing."