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COMPUTING SCIENCE

The Computer and the Dynamo

Brian Hayes

Personal Virtues

For Huber and Mills, the power demands of computers and the Internet signal inevitable future growth in overall electricity consumption. But you can equally well look at the situation as an opportunity for conservation. If computers really were responsible for some large fraction of the nation's energy consumption, then measures to make the machines more efficient would have a major impact. And even if computers do not make up such a fat slice of the energy pie, they may nonetheless be an attractive target for conservation measures, because there's so much room for improvement. Cutting another 10 percent off the energy consumption of a refrigerator or a water heater is an engineering challenge, but the energy per operation and per device in computers has been falling for decades, and that trend will surely continue. Indeed, there is no intrinsic limit to it; in principle, computing can be done without energy loss.

In the 1940s, the ENIAC had 18,000 vacuum tubes and consumed 174 kilowatts—roughly 10 watts per tube. If modern silicon chips required 10 watts per transistor, a Pentium would suck 100 megawatts out of the power grid, and the computer on your desk would easily swallow the entire output of a nuclear plant. Instead, a few tens of watts are enough to power a chip with transistors numbering in the tens of millions.

For the most part, these gains in transistor efficiency have been exploited not to minimize the power consumption of each chip but to maximize the number of transistors per chip, while keeping the power density just below the melting point. There is little incentive to do otherwise. This is the muscle-car era of computer design; what sells hardware is performance, not fuel economy. Until the electric bill for running a machine begins to approach the purchase price, no one is going to care much about energy consumption.

But energy use in computers may well decline anyway, even without economic impetus. Laptop computers offer a proof by example that electric power can be reduced by an order of magnitude without greatly impairing computer power. Some of the technologies and components of laptops will find their way into desktop machines, again not because lower power consumption is a selling point but because smaller fans, heat sinks and power supplies can save the manufacturer a few dollars. Flat-panel displays are already migrating from laptops to desktops.

Power-management systems that put idle machines and monitors to sleep have also had an effect. In the 2000 office-equipment survey, Koomey and his colleagues find that such reduced-power modes save 23 terawatt-hours per year; if everyone used the sleep modes, they would save another 17 terawatt-hours.

At the end of the day, I am left with the sense that the issue of computer power consumption is not going to be the determining factor in national energy policy. Even if the Huber-Mills analysis were correct, most of our kilowatts would still be flowing into the real world, not into cyberspace. Fluctuations in prices and the weather have a bigger impact on power demand than any conceivable events on the World Wide Web. Computers will not save the coal mines, nor will they save the planet.

But efficiency is more than a matter of economics and industrial policy; it has an aesthetic aspect, and even an ethical one. As Vice President Cheney recently observed, energy conservation is a sign of personal virtue. There is satisfaction in accomplishing more with less, in wringing the most results out of the least resources. For a long time this was a prominent strand in the mental habits of computer enthusiasts. To waste a CPU cycle or a byte of memory was an embarrassing lapse. To clobber a small problem with a big computer was considered tasteless and unsporting, like trout fishing with dynamite. Not even rolling blackouts will roll us back to that quaint age of frugal computing, but there is much to admire in its ethos.

© Brian Hayes





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