Changing Phases

February 1996 / Reviews / CD-ROM Has a New MO / Changing Phases

Phase-change technology is just now reaching the mass market, although the process has been under development for a number of years. On the surface, phase change is simple. The recording head directs a tiny, multiple-energy-level laser across the disc. The normal state for the recording layer is amorphous, which provides one set of reflective characteristics. When heated to a precise temperature, the material transitions to a crystalline state with a different reflectiveness. The drive head reads the different states as ones and zeros.
To write over existing data, the laser heats the spot to the material's melting point. After melting, the material cools not to the crystalline state but back t o the amorphous state. Controlling the head movement and laser position requires highly sensitive control mechanisms.

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Matthew Wilson
My approach to software engineering is far more pragmatic than it is theoretical--and no language better exemplifies this than C++.

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