Philip Schiller, Apple's senior vice-president of worldwide marketing, admits he was stunned by the audacity of Virginia Tech's concept. Until then, Apple hadn't been a serious player in big-time supercomputing, even though so-called cluster supercomputers -- clumps of wired-together personal computers built with chips from Advanced Micro Devices (AMD ), Intel (INTC ), IBM, and Sun Microsystems (SUNW ) -- had been the hottest breed of "super" for more than a decade.

TOP500 ENTHUSIASM.  Up to that point, Apple's cluster entries had been mainly low-end systems, such as the 56-computer PowerMac G4 cluster assembled in 2002 by University of California at Los Angles physicists, and UCLA's earlier, smaller Macintosh G3 clusters. What impressed the UCLA researchers was how easy a bunch of Macs could be roped together. They developed software to do the setup in hours, not the days or even weeks typically needed to create a Linux cluster of PCs.

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The tight-knit supercomputing community was surprised by what Virginia Tech and Apple pulled out of their hat -- and impressed. It didn't take long for others to jump on the Big Mac wagon. The newest system aims to one-up Virginia Tech by linking 1,566 G5 Xserve units. Dubbed Mach 5 and being built by Colsa Corp. in Huntsville, Ala., this cluster will have a theoretical peak speed of more than 25 teraflops.

That would earn the No. 2 spot on the Top500 list that was issued in June. Only Japan's Earth Simulator, built by NEC (NIPNY ) and rated at 41 peak teraflops, is faster -- although it and Mach 5 may soon be overtaken by clusters now a-building by longtime super suppliers IBM and Cray (CRAY ).

COOL ADVANTAGE.  Mach 5 is slated to go into service this fall at the Army Research & Development Command's Aviation & Missile Research, Development & Engineering Center in Huntsville. It will do nothing but run one job: simulating hypersonic flight. Currently, the center uses an aging IBM supercomputer with 284 processors, and each simulation chews up a solid month of computing time. With Mach 5, says Anthony C. DiRienzo, executive vice-president at Colsa, "they'll be able to do a new run every day, overnight."

DiRienzo figures Apple can count on lots more supercomputer business. None of the other vendors that bid on the Army job, he explains, came close to matching Apple's price/performance ratio. The hardware was only $5.8 million -- 60% of the speed of Earth Simulator for 1.5% of its $400 million cost. "But what's really nice about the G5 pizza-box-size servers," he says, "is how well they dissipate heat." Apple's engineering stood head and shoulders above the competition on this score.