IBM announced this week that it is using a new way of making magnetic disk drives that will vastly increase the amount of data they can hold. The technology pushes back what some industry insiders had long considered a fundamental limit to the density of magnetic data. The switch is expected to quadruple data capacity to about 100 billion bits per square inch by 2003, a density that will allow desktop computers to store 400 gigabytes of data.
Company officials say they are making the switch because conventional magnetic data-storage technology is nearing the end of its rope. That technology stores a "bit" of data--a computer's digital ones and zeros--as the common magnetic orientation of hundreds of tiny grains in a thin layer of magnetic material atop a circular platter. Over the last 45 years, engineers have packed more such bits in a given area of disk space by shrinking the magnetic grains, among other techniques. But with those grains now just a few tens of atoms across, they are so small that their magnetic hold is weak: Ambient heat can cause them to flip their magnetic orientation, which erases the stored information.
To overcome the problem, IBM engineers have switched to what they call "antiferromagnetically coupled media" made up of three layers. The first, a thin layer of a conventional magnetic alloy, is topped with a layer of ruthenium just three atoms thick, and a thicker magnetic alloy is deposited on top. A magnetic interaction between grains above and below the ruthenium causes the magnetic fields in these grains to point in opposite directions. The result is that heat and other stresses have a harder time flipping bits, because for a stress to flip the magnetic orientation of a grain in the top layer, it would also have to have enough energy to flip the one below it in the opposite direction.
"It's a very clever idea to get more robust bits at a given density," says David Awschalom, a physicist at the University of California, Santa Barbara. IBM is already using the new technology to make its top-of-the-line notebook disk drives, which it began shipping several weeks ago, and is in the midst of switching all its drives to the new technology.