In the computer revolution, the optical disk is poised to be the all-purpose storage medium of choice. But before it can fulfill this heady role, it will have to store a whole lot more information than it does today.
Nowadays the zeros and ones of digital information are carved into the surface of a plastic disk as a string of microscopic marks and spaces. As the disk spins under a laser beam, the beam, if it encounters a space, reflects off a shiny aluminum backing behind the semitransparent plastic and triggers a photodetector. When the beam encounters a mark, on the other hand, it scatters. Hal Rosen, a staff member at IBM’s Research Division in San Jose, California, woke up one morning with a simple but powerful idea that builds on this technology. Rosen thought of layering marks and spaces. First he removed the aluminum backing. The plastic still reflected a small amount of light. Then, with a lens directing the laser beam to a specific layer and reading the reflected light, the photodetector could be made to select one level at a time while ignoring the others.
The technique, it turns out, works with any kind of optical disk, though IBM will apply it first to disks for holding computer data. So far, Rosen and colleagues have made optical disks with 6 levels of storage, but we don’t see why we can’t do 20 levels, he says. By adding higher- frequency lasers and new methods of compressing data, Rosen believes he can eventually put 100 billion bytes of information onto a small disk--more than enough for several full-length motion pictures, a whole day’s worth of music, or reams of computer data. Or, says Rosen, with one of these disks you could have a small public library on your desktop.
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