CD-RW (Compact Disc-Rewritable) is a
digital Digital usually refers to something using discrete digits, often binary digits. Technology and computing Hardware *Digital electronics, electronic circuits which operate using digital signals **Digital camera, which captures and stores digital i ...
optical disc In computing and optical disc recording technologies, an optical disc (OD) is a flat, usually circular disc that encodes binary data (bits) in the form of pits and lands on a special material, often aluminum, on one of its flat surfaces. ...
storage format introduced in 1997. A CD-RW
compact disc The compact disc (CD) is a digital optical disc data storage format that was co-developed by Philips and Sony to store and play digital audio recordings. In August 1982, the first compact disc was manufactured. It was then released in October ...
(CD-RWs) can be written, read, erased, and re-written. CD-RWs, as opposed to CDs, require specialized readers that have sensitive laser optics. Consequently, CD-RWs cannot be read in many CD readers built prior to the introduction of CD-RW. CD-ROM drives with a "MultiRead" certification are compatible. CD-RWs must be erased or blanked before reuse. Erasure methods include full blanking where the entire surface of the disc is erased and fast blanking where only metadata areas, such as PMA, TOC and pregap, are cleared. Fast blanking is quicker and usually sufficient to allow rewriting the disc. Full blanking removes all traces of the previous data, and is often used for confidentiality purposes. CD-RWs can sustain fewer re-writes compared to other storage media (ca. 1,000 compared up to 100,000). Ideal use is for test discs (e.g. for CD authoring), temporary backups, and as a middle-ground between online and offline storage schemes.


Before CD-RW technology, in 1990 a standard for magneto-optical recordable and erasable CDs called CD-MO was introduced and set in the Orange Book, part 1 as a CD with a magneto-optical recording layer. 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. Dy Fe Co or less often Tb Fe Co or Gd Fe Co) to its
Curie point In physics and materials science, the Curie temperature (''T''C), or Curie point, is the temperature above which certain materials lose their permanent magnetic properties, which can (in most cases) be replaced by induced magnetism. The Cur ...
and then using a magnetic field to write the new data, in a manner essentially identical to Sony's
MiniDisc MiniDisc (MD) is an erasable magneto-optical disc-based data storage format offering a capacity of 60, 74, and later, 80 minutes of digitized audio. Sony announced the MiniDisc in September 1992 and released it in November of that year for ...
and other magneto-optical formats. Reading the discs relied on the
Kerr effect The Kerr effect, also called the quadratic electro-optic (QEO) effect, is a change in the refractive index of a material in response to an applied electric field. The Kerr effect is distinct from the Pockels effect in that the induced index cha ...
a major format flaw. The rewrite could only be read in special drives and was incompatible with non-magneto-optical enabled drives. The format was never released commercially,Upgrading and repairing PCs
By Scott Mueller, page 739: "The Orange Book comes in three parts: Part I describes a format called CD-MO (magneto-optical), which was to be a rewritable format but was withdrawn before any products really came to market"
mostly because of incompatibility with standard CD reading units. Early
CD-R CD-R (Compact disc-recordable) is a digital optical disc storage format. A CD-R disc is a compact disc that can be written once and read arbitrarily many times. CD-R discs (CD-Rs) are readable by most CD readers manufactured prior to the int ...
media contained a similar compatibility flaw. Since the CD-MO was otherwise identical to CDs, the format still adopted a spiral-groove recording scheme, rendering the disc poorly suited as a removable medium for repeated, small-scale deletions and recordings. Some magneto-optical drives and media with the same form factor don't 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. The early introduction and no standards for disc recording software, file systems, and formats, physical incompatibility, coupled with more economical CD-R discs, led to abandoning the format. Other magneto-optical media, unbound by limitations of the typical CD-ROM filesystems, replaced the CD-MO.

Mechanism of action

Rewritable media can, with suitable hardware, be re-written up to . The CD-RW is based on phase change technology, with a degree of reflection at , compared to for CD-R discs. 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 A sine wave, sinusoidal wave, or just sinusoid is a mathematical curve defined in terms of the '' sine'' trigonometric function, of which it is the graph. It is a type of continuous wave and also a smooth periodic function. It occurs often i ...
excursion of at a frequency of . In addition a
frequency modulation Frequency modulation (FM) is the encoding of information in a carrier wave by varying the instantaneous frequency of the wave. The technology is used in telecommunications, radio broadcasting, signal processing, and computing. In analog freq ...
is applied to provide the recorder with an absolute time reference. Groove width is and pitch of . The media for CD-RW has the same layers as CD-R media. The reflective layer is, however, a silver-
indium Indium is a chemical element with the symbol In and atomic number 49. Indium is the softest metal that is not an alkali metal. It is a silvery-white metal that resembles tin in appearance. It is a post-transition metal that makes up 0.21 parts p ...
antimony Antimony is a chemical element with the symbol Sb (from la, stibium) and atomic number 51. A lustrous gray metalloid, it is found in nature mainly as the sulfide mineral stibnite (Sb2S3). Antimony compounds have been known since ancient times ...
- tellurium (
AgInSbTe AgInSbTe, or silver-indium-antimony-tellurium, is a phase change material from the group of chalcogenide glasses, used in rewritable optical discs (such as rewritable CDs) and phase-change memory applications. It is a quaternary compound of silv ...
) alloy with a
polycrystal A crystallite is a small or even microscopic crystal which forms, for example, during the cooling of many materials. Crystallites are also referred to as grains. Bacillite is a type of crystallite. It is rodlike with parallel longulites. Stru ...
line structure and reflective properties in its original state. When writing the laser beam uses its maximum power () to heat the material to causing material
liquefaction In materials science, liquefaction is a process that generates a liquid from a solid or a gas or that generates a non-liquid phase which behaves in accordance with fluid dynamics. It occurs both naturally and artificially. As an example of the ...
. In this state, the alloy loses its polycrystalline structure and reflectivity and assumes an
amorphous In condensed matter physics and materials science, an amorphous solid (or non-crystalline solid, glassy solid) is a solid that lacks the long-range order that is characteristic of a crystal. Etymology The term comes from the Greek ''a'' ("wit ...
state. The lost reflectivity serves the same function as bumps on manufactured CDs and the opaque spots on a CD-R are read as a ''0''. The polycrystalline state of the disc forms the trenches, which are read as ''1''. The scanning signal when reading is created by strong or weak reflection of the laser beam. To erase the disc, the write beam heats the amorphous regions with low power to about . The alloy is not melted, but returns to the polycrystalline state and is again reflective.


During and after a disc authoring the distribution of data on the CD-RW varies. The following areas are present: *PCA: The Power Calibration Area is used to determine the correct power level for the laser. *PMA: The Program Memory Area of a CD-RW is a record of the data recorded on an unfinished or unfinalized disc. It is used as a transition TOC while the session is still open. PMA records may contain information on up to 99 audio tracks and their start and stop times (
CD-DA Compact Disc Digital Audio (CDDA or CD-DA), also known as Digital Audio Compact Disc or simply as Audio CD, is the standard format for audio compact discs. The standard is defined in the ''Red Book'', one of a series of Rainbow Books (named fo ...
), or sector addresses for the start of data files for each session on a data CD. *PA: The Program Area contains the audio tracks or data files. *SUA: The System User Area The PCA and the PMA grouped together are sometimes denoted as the System User Area. Each session on a multi-session disc has a corresponding lead-in, PMA, PA and lead-out. When the session is closed TOC information in the PMA is written into a lead-in area and the PCA and PMA are logically eliminated. The lead-out is created to mark the end of the data in the session.

Speed specifications

Like a CD-R, a CD-RW has hardcoded speed specifications which limit recording speeds to fairly restrictive ranges. 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 A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word "laser" is an acronym for "light amplification by stimulated emission of radiation". The firs ...
energy levels. Despite this, some professional audio CD recorders, such as those made by Tascam, use special techniques to bypass these limitations and can record high speed (but not ultra speed) discs in realtime. 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 written. Similarly, using inappropriately high amounts of laser energy will cause the material to overheat and be ''insensitive'' to the data, a situation typical of slower discs used in a high powered and fast specification drive. For these reasons, older CD-RW drives that lack appropriate firmware and hardware are not compatible with newer, high-speed CD-RW discs, while newer drives can record to older CD-RW discs, provided their firmware correct speed, delay, and power settings can be appropriately set. The actual reading speed of CD-RW discs, however, is not directly correlated or bound to speed specification, but depends primarily on the reading drive's capabilities. Many half-height CD and DVD writers released between 2004 and 2010, including the '' TSSTcorp SH-M522'' combo drive (2004), Pioneer ''DVR-110D'' (2005),Pioneer DVR-110D DVD Multi writer specification sheet
/ref> Hitachi-LG ''GSA-4167'' (2005)'','' TSSTcorp ''SH-S182/S183'' (2006) and ''SH-S203/TS-H653B'' (2007) have officially adapted support for CD-RW ''UltraSpeed Plus'' (32×
Z-CLV In optical storage, constant linear velocity (CLV) is a qualifier for the rated speed of an optical disc drive, and may also be applied to the writing speed of recordable discs. CLV implies that the angular velocity (i.e. rpm) varies during an o ...
), while more recent DVD writers such as the ''SH-224DB'' (2013) and Blu-Ray writers such as the '' LG BE16NU50'' (2016) have downgraded the
backwards compatibility Backward compatibility (sometimes known as backwards compatibility) is a property of an operating system, product, or technology that allows for interoperability with an older legacy system, or with input designed for such a system, especially i ...
to CD-RW ''UltraSpeed'' (24× Z-CLV).Archive of discontinued Hitachi-LG Data Storage optical drives
/ref>Archive of TSSTcorp optical drive manuals
/ref> '' Slim type'' optical drives are subject to physical limitations, thus are not able to attain rotation speeds of half-height (desktop) optical drives. They usually support CD-RW writing speeds of 16×HL-DT-ST BU20N specification sheet
/ref> or 24× Z-CLV in zones of 10× CLV, 16× CLV, 20× CLV and 24× CLV towards the outer edge, of which the highest speed zone depends on availability.LiteOn eTAU108 - DVD±RW (±R DL) / DVD-RAM drive - Hi-Speed USB Series Specification sheet and picture
-, 2009; accessed July 11th 2020.

See also

* List of optical disc manufacturers


* Bennett, Hugh. "CD-E: Call it Erasable, Call it Rewritable, but will it Fly?" ''CD-ROM Professional'' Sept. 1996: 28+ * Bennett, Hugh. ''Understanding CD-R & CD-RW''. Cupertino: Optical Storage Technology Association, Jan. 2003. * Steinmetz, Ralf and Nahrstedt, Klara. "Multimedia Fundamentals Volume 1: Media Coding and Content Processing", .

External links

ECMA-395: Recordable Compact Disc Systems CD-RW Ultra-Speed
(standardized Orange Book, Part III, Volume 3)

{{DEFAULTSORT:Cd-Rw Audiovisual introductions in 1997 Audio storage Compact disc Video storage Optical computer storage media