WORM (write once, read many) Definition

In computer storage media, WORM (write once, read many) is a data storage technology that allows information to be written to a disc a single time and prevents the drive from erasing the data. The discs are intentionally not rewritable, because they are especially intended to store data that the user does not want to erase accidentally. Because of this feature, WORM devices have long been used for the archival purposes of organizations such as government agencies or large enterprises. A type of optical media, WORM devices were developed in the late 1970s and have been adapted to a number of different media. The discs have varied in size from 5.25 to 14 inches wide, in varying formats ranging from 140MB to more than 3 GB per side of the (usually) double-sided medium. Data is written to a WORM disc with a low-powered laser that makes permanent marks on the surface.

Because of a lack of standardization, WORM discs have typically been only readable by the drive on which they were written, and hardware and software incompatibility has hampered their marketplace acceptance. Other optical media, such as CDs and DVDs that can be recorded once and read an unlimited number of times are sometimes considered WORM devices, although there is some argument over whether formats that can be written in more than one session (such as the multisession CD) qualify as such. CD-R has gradually been replacing traditional WORM devices, and it is expected that some newer technology, such as DVD-R or HD-ROM will eventually replace both WORM and CD-R devices.