In the old days, computer vendors would often pull a fast one. They would tell you their system had the latest microprocessor when it actually had a cheaper, slower version running faster than the chip’s rating permitted. So the shiny, new 500-megahertz system you thought you were buying might contain only an overclocked 300-MHz CPU. But the computer worked fine; indeed, it might have operated perfectly for years, with you none the wiser. And you perhaps replaced it only because a good buy on a 1-gigahertz machine eventually came along.

How did that poor 300-MHz processor cope with such abuse? The short answer is that the manufacturer had set the clock speed low to ensure that its products would function without fault despite the inevitable variations among chips and among their different operating environments. Shady overclockers took advantage of that conservatism, inviting unpredictable failures when they eliminated the chipmaker’s prudent safety margins.

Lately, overclocking has gone mainstream. You can, for example, find competitions on the Web in which hardware hackers vie for top honors in this domain. Even chip manufacturers themselves are doing it in public trials to show off how blazingly fast their processors can run under the right conditions—like when they are being cooled with liquid helium to within a few kelvins of absolute zero.

Engineers at Advanced Micro Devices, of Sunnyvale, Calif., did just that this past April to prove that the company’s Phenom II CPU could break the 7-GHz barrier. In theory, they could have used the same approach to reduce the voltage at which this chip runs at its normal clock speed. That in turn would have significantly diminished the power it consumed.

While saving a few watts is not so important in a desktop system, it’s critical for smartphones, mobile Internet devices, and other such gadgetry, which now have to handle glitzy graphics, video, Web access, and gaming without burning too quickly through their tiny batteries. And reducing the amount of power that a CPU uses translates to an enormous amount of money saved for the companies that deploy vast numbers of microprocessors in large-scale server farms.

The problem is that if you use anything less than their normal voltage, some of these chips, on rare occasions, will fail to produce the correct results. That might happen when a laptop is turned on after being left to bake in a hot car, for example. The resulting miscalculations could be catastrophic—or maybe not.

What if a microprocessor could check its output and correct any error on the fly? Suppose further that the chip could slow itself down or turn up its voltage slightly when it noticed it was flubbing up too often. Experiments we and our colleagues at the University of Michigan in Ann Arbor have carried out show that adding those capabilities to a microprocessor can slash energy use by more than a third.