Library Technology Guides

A videodisk that can be erased and rerecorded has been announced by the Japan Broadcasting Corp. (Tokyo), thus overcoming a major limitation of current videodisk systems. The Japanese prototype uses a helium-neon laser to write data on a disk coated with a magnetic film of amorphous gadolinium and cobalt. Data is recorded when the heat from the laser beam causes local reversals of the film's magnetic field. New data can be written over old data, or the entire disk can be erased by bathing it in a strong magnetic field. In contrast, conventional systems do now allow rerecording or erasure because the laser in these systems punches holes--representing data--in the disk coating. The erasable system, which also uses a laser to read data via an optomagnetic effect, needs further development to overcome a low signal-to-noise ratio and disk coating imperfections that cause data loss.