Reversible computing raises the bar for chips

BANGALORE: The goal of reversible computing is to re-engineer the integrated circuits that perform all computing operations to re-use, or recycle, most of the large amount of wasted energy they currently throw off in the form of heat. So-called “reversible computing” would not only reduce computer chips’ power consumption, it also could boost their speed, because these chips are becoming so fast that the heat they generate limits the speed at which they can operate without overheating and malfunctioning.

The research comes at a time when computers are estimated to consume as much as 10 percent of electricity in the United States, and chips are rapidly reaching the upper limits of their heat tolerance, said Michael Frank, a UF assistant professor of computer and information science and engineering.

“The fastest processors available today dissipate on the order of 100 watts of power in the form of heat,” or about as much as a large light bulb, he said. “The main reason you can’t run them faster is because they get too hot. If you could make them produce less heat in the first place, you could end up running them faster overall, especially if you want to pack a lot of chips together.”

Frank, who first worked on reversible computing as a doctoral student at the Massachusetts Institute of Technology, heads UF’s Reversible & Quantum Computing Research Group.

Reversible computing, the intellectual seeds of which date back to the early 1960s, means setting up logic operations -- which manipulate the 0s and 1s at the core of digital computation -- so they can be undone or reversed. The process differs from the current approach, which performs operations but later discards the result. For example, when a computer “erases” something, what it does physically is ground one part of a circuit that holds a charge, in effect converting the stored energy -- and the information it represents -- into heat, Frank said. When chips perform millions or billions of erasing and other operations in a short time, the total heat becomes substantial, limiting both the performance of the chip and the number of chips that can be packed together in a small space, he said.

In fact, unless reversible computing is achieved, computer chips are expected to reach their maximum performance capabilities within the next three decades, effectively halting the rapid advances in speed that have driven the information technology revolution, Frank said. “Reversible computing is absolutely the only possible way to beat this limit,” he said.

Reversible computing seeks to configure integrated circuits in such a way that they can use their current state to recover previous states - in other words, rather than building up and tossing away unwanted information, the chips “uncompute” it fluidly, with little power expenditure or heat generation. Researchers hope to achieve such results by incorporating tiny oscillators, or spring-like devices, in the circuits. In theory, these oscillators could recapture most of the energy expended in a calculation and reuse it other calculations. The concept is somewhat analogous to hybrid cars now on the market that take the energy generated during braking and recycle it into electricity used to power the car.

“Rather than throwing away all the circuit’s energy constantly, it essentially bounces back and forth, in a more elastic fashion,” Frank said.