CD-RW is a digital optical disc storage format. A CD-RW disc is a disc that can be written, read arbitrarily many times, erased. The technology was introduced in 1997, CD-RW discs require readers that have more sensitive laser optics than are required to read plain CDs. Consequently, CD-RWs cannot be read in many CD readers built prior to the introduction of CD-RW, CD-ROM drives that bear a MultiRead certification claim compatibility. CD-RW discs need to be blanked before reuse, fast blanking is much quicker, and is usually sufficient to allow rewriting the disc. Full blanking removes traces of the data, often for confidentiality reasons. It may be possible to data from full-blanked CD-RWs with specialty data recovery equipment, however. Their ideal usage field is in the creation of test discs, temporary short or mid-term backups, and in general, the CD-MO standard also allowed for an optional non-erasable zone on the disc, which could be read by normal CD-ROM reader units. Reading of the discs relied on the Kerr effect, the format was never released commercially, mostly because of its inherent incompatibility with standard CD reading units. A similar situation was present for early CD-R media, which suffered from either physical or logical incompatibilities. There were however some magneto-optical drives and media with the form factor that dont have this limitation. Unlike modern CD-RWs, CD-MO allowed for hybrid discs containing both an unmodifiable, pressed section, readable in standard drives, and a writable MO section, other kinds of magneto-optical media, unbound by the limitations of the typical CD-ROM filesystems, took the place intended for CD-MO. Rewritable media can, with hardware, according to some manufacturers. The CD-RW technology is based on phase change technology, so the degree of reflection reached is only 15–25%, the properties of the medium and the write and erase procedure is defined in the Orange Book Part III. To keep rotational speed precise, tracks have a slight superimposed sinusoidal excursion of 0.3 µm at a frequency of 22.05 kHz, in addition a 1 kHz frequency modulation is applied to provide the recorder with an absolute time reference. The grooves have a width of 0.6 µm and pitch of 1.6 µm, the media for CD-RW has basically the same layers as CD-R media. The reflective layer is, however, an alloy, which has in its original state. When writing the laser beam uses its power to heat the material to 500–700 °C
Compact Disc ReWritable (CD-RW) logo/trademark
Philips created the "High-Speed" CD-RW logo for media that supports writing speeds above 4×.