Saving energy by tolerating mistakes

Computer chips can use significantly less energy if they don’t have to be correct all the time. That’s the idea behind PCMOS — probabilistic complementary metal-oxide semiconductor technology. Here’s an excerpt from Technology Review’s article on PCMOS.

[Inventor Krishna] Palem’s idea is to lower the operating voltage of parts of a chip—specifically, the logic circuits that calculate the least significant bits, such as the 3 in the number 21,693. The resulting decrease in signal-to-noise ratio means those circuits would occasionally arrive at the wrong answer, but engineers can calculate the probability of getting the right answer for any specific voltage. “Relaxing the probability of correctness even a little bit can produce significant savings in energy,” Palem says.

In applications such as video processing, a small probability of error would not make a noticeable difference. It would be an interesting exercise to separate those parts of a system that require accuracy and those that tolerate error. For example, a cell phone might use high-accuracy chips for dialing phone numbers but low-accuracy chips for controlling the display in order to extend battery life.

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