Write-once, read-many

Definition
A write-once, read-many (WORM) is an optical media storage system first introduced in the early 1980s. WORM processes record data by means of a laser beam permanently altering the reflective characteristics of the disk's recording surface or sensitized layer(s).

Overview
WORM optical recording technology processes include ablative, thermal bubble, bimetallic alloy, dye-polymer, and phase change.


 * The ablative process, the earliest commercially available optical recording technology, alters the optical digital data disk's reflective characteristics by creating submicron-sized pits, or bubbles, to indicate 1's and 0's.
 * Thermal bubble recording creates bubbles on the optical media's surface using the laser beam's concentrated energy.
 * 'Bimetallic technology uses a laser beam to fuse several alloys together into a totally new alloy with a different reflective index.
 * In the dye-polymer and phase change recording technologies, the laser beam alters the media's physical color and reflective characteristics, with the information signified by the color changes.

Because these recording technologies involve a non-reversible physical alteration of the recording surface, they are designated "write once."