CD-RW

RW (Compact Disc-Rewritable) is a digital optical disc storage format introduced by Ricoh in 1997.

They are ideally used for test discs (e.g. for CD authoring), temporary backups, and as a middle-ground between online and offline storage schemes.

The CD-MO standard allowed for an optional non-erasable zone on the disc that could be read by CD-ROM units.

Data recording (and erasing) was achieved by heating the magneto-optical layer's material (e.g. DyFeCo or less often TbFeCo or GdFeCo) to its Curie point and then using a magnetic field to write the new data, in a manner essentially identical to Sony's MiniDisc and other magneto-optical formats.

The CD-RW is based on phase change technology, with a degree of reflection at 15–25%,[6] compared to 40–70% for CD-R discs.

[6] The properties of the medium and the write and erase procedure is defined in the Orange Book Part III.

To maintain a precise rotation speed, tracks have a slight superimposed sinusoidal excursion of 0.3 µm at a frequency of 22.05 kHz.

[6] In addition a 1 kHz frequency modulation is applied to provide the recorder with an absolute time reference.

Unlike a CD-R, a CD-RW has a minimum writing speed under which the discs cannot be recorded, based on the phase change material's heating and cooling time constants and the required laser energy levels.

[citation needed] Since the CD-RW discs need to be blanked before recording data, writing too slowly or with too low energy on a high speed unblanked disc will cause the phase change layer to cool before blanking is achieved, preventing the data from being properly written.