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An Apple so hot it's liquid-cooled

Apple Computer's new top-of-the-line G5 Power Mac is the company's hottest computer yet. Which explains the water pump.

Liquid cooling isn't a feature you'll find on many computers, but Apple likes to stay out in front. Indeed, the company is touting its new liquid-cooled machine as an engineering triumph. Perhaps it is, but it is one born of necessity. The dual microprocessors that drive the new G5 run hot -- so hot that the old cooling system was no longer adequate.

''You need something that's more efficient than a traditional copper heat sink," said Tom Boger, Apple's senior director of desktop product marketing.

Hence the adoption of a cooling technique that seems better suited to a V8 than a PC.

Apple isn't the only company that's starting to sweat. Intel Corp., the world's top chip maker, turned up the thermostat with its newest Pentium 4 chips. One version, code-named Prescott, is an exceptionally hot piece of silicon. According to Anandtech, a website that publishes in-depth reviews of computer systems, Prescott runs about 20 degrees hotter than a high-end product from Intel's rival, Advanced Micro Devices Inc. To celebrate, AMD last week sent journalists a ''Prescott survival kit," complete with an oven mitt, a cooling fan, and a sales pitch for AMD's cooler chips.

It's all fun and games, until your motherboard starts to melt. And that could happen unless chip makers solve their heat problem.

It's not a new issue, actually. People used water to cool computers in the era of house-size mainframes. Back then, machines used ''bipolar" transistors that gave off vast amounts of heat. Starting in the 1980s, all kinds of computers, from mainframes to desktops, switched to a different, cooler transistor design, and liquid cooling was mostly confined to high-performance supercomputers.

But the heat problem is back, thanks to the chip makers' determination to obey Moore's Law. You know that one -- the rule that says the number of transistors on a chip should double every 18 months. You could do this by making the chips bigger, but that makes them more costly, because you'd get fewer chips from every silicon wafer. It would also slow down the chips, by making the circuit paths longer.

Instead, chip designers cram more transistors into the smallest possible area, which accounts for the phenomenal improvements in computer speed we now take for granted. But this also means squeezing millions more transistors closer and closer together. It takes power to drive each transistor, and that power is ultimately radiated away as heat. An Intel Prescott has 125 million transistors, over twice as many as the previous Pentium 4, in an area smaller than your thumbnail. The result is a chip that literally has power to burn.

Something has to give. So chip makers are seeking ways to make their products run cooler -- or at least no hotter --while PC builders investigate ever more esoteric ways to carry off the waste heat.

Intel and AMD are doing their part by embracing the ''dual-core" concept. Both companies say their future chips will feature two processors on a single piece of silicon. Instead of making one ultra-powerful, ultra-hot chip, the companies will etch two sort-of-powerful processors into the silicon, then link them. Programs will be executed in pieces, with each core carrying part of the load. This kind of parallel computing isn't easy to manage, but for many tasks it should allow a pair of cooler and slower processors to work as well as a fast, hot chip.

Even so, the heat problem will persist, forcing PC makers to devise creative cooling strategies. For example, they're working on improvements to the thermal grease that's smeared between the chip and its heat sink. This goop ensures a snug fit, which is vital to correct heat transfer. Chemists are studying whether compounds containing nanoparticles or even soot would do a better job.

But lots of PC makers will probably follow Apple's lead and embrace liquid cooling. Their hearts won't be in it; Apple doesn't mind charging $3,000 for its G5, but most PC firms sell low-cost boxes with skimpy profit margins. Michael Dell won't be keen on adding the cost of a water pump to each machine.

It's a good thing smart people are looking for cheaper alternatives. Cooligy Inc., of Mountain View, Calif., says it has figured out a way to pump water over a chip without using a pump. Cooligy uses an electrical current to pull ionized water through glass tubes. Its scientists got the best results from tubes made of glass granules used to filter beer.

''We name all of our pumps after beers," said Cooligy's president, Dave Corbin. ''We have Asahi, we have Guinness, we have Sam Adams."

The US Defense Advanced Research Projects Agency gave Cooligy about $4 million to develop the technology, which is based on research done at Stanford University. Corbin said his company's pumps should hit the market next year. They can be scaled to work in any kind of computer. And since there's no mechanical pump, the system will be cheap to install and maintenance-free. Quiet, too.

Apple geeks will get a headstart on liquid cooling when the G5 debuts next month, but the rest of us will probably catch up in the next year or two. After all, computer chips aren't getting any slower -- or cooler.

Hiawatha Bray can be reached at bray@globe.com.

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