CD-RW

A CD-RW (Compact Disc-ReWritable) is a rewritable optical disc. It was introduced in 1997, and was known as "CD-Writable" during development. It was preceded by the CD-MO, which was never commercially released.

CD-RW disc require a more sensitive laser optics. Also, CD-RWs cannot be read in some CD-ROM drives built prior to 1997. CD-ROM drives will bear a "MultiRead" certification to show compatibility. CD-RW discs need to be blanked before reuse. Different blanking methods can be used, including "full" blanking in which the entire surface of the disc is cleared, and "fast" blanking in which only meta-data areas are cleared: PMA, TOC and pregap, comprising a few percent of the disc. Fast blanking is much quicker, and is usually sufficient to allow rewriting the disc. Full blanking removes traces of the former data, often for confidentiality. It may be possible to recover data from full-blanked CD-RWs with specialty data recovery equipment; however, this is generally not used except by government agencies due to cost.

CD-RW also have a shorter rewriting cycles life (ca. 1,000) compared to virtually all of the previously exposed types storage of media (typically well above 10,000 or even 100,000), something which however is less of a drawback considering that CD-RWs are usually written and erased in their totality, and not with repeated small scale changes, so normally wear leveling is not an issue.

Their ideal usage field is in the creation of test disks, temporary short or mid-term backups, and in general, where an intermediate solution between online and offline storage schemes is required.