THE GOOD OLD HARD-DISK drive is showing more longevity than seemed possible in the 1980s. IBM, which set a record in 1989 by cramming 1 billion bits of data onto one square inch of disk surface, announced on Mar. 30 that it had boosted its world record to 3 billion bits--or 3 gigabits. That's nearly five times the density of the most advanced commercial disk drive: IBM's Travelstar LP 2.5-inch drive for subnotebook computers.

Vincent Marrello, manager of recording heads at IBM's Almaden Research Center in San Jose, Calif., attributes the latest advance to "exquisite engineering" rather than some experimental technology. Engineers improved the cobalt-alloy recording surface, he says, by laying it down in a way that produces fine magnetic grains that still behave independently. They also shrank the heads that read and write (photo) to handle smaller bits. The head that reads works on the principle that electrical resistance fluctuates in varying magnetic fields. IBM is the only company mass-producing these so-called magnetoresistive heads.

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