A type of rewritable optical disk that employs the phase change recording method. Using this technique, the disk drive writes data with a laser that changes spots on the disk between amorphous and crystalline states. An optical head reads data by detecting the difference in reflected light from amorphous and crystalline spots. A medium-intensity pulse can then restore the original crystalline structure.
Magneto-optical and dye-polymer technologies offer similar capabilities for developing re-writable optical disks.