View source for CD-RW

{{Short description|Optical disk technology}}
{{Use American English|date=February 2025}}
{{more citations needed section|date=February 2019}}

[[File:CDRW-Logo.svg|thumb|Logo of Compact Disc-ReWritable (CD-RW).]]
[[File:CD-RW bottom.jpg|thumb|CD-RW with distinctively darker data surface than a [[CD-R]] and a factory-pressed [[CD-ROM]].]]
{{Optical disc authoring}}


'''RW''' ('''Compact Disc-Rewritable''') is a [[digital media|digital]] [[optical disc]] [[data storage device|storage]] format introduced by Ricoh in 1997.<ref>{{cite journal|date=August 1997|journal=	Library Systems Newsletter|title= Ricoh shows CD-RW hardware|url=https://librarytechnology.org/document/5608/|access-date=November 1, 2024| volume= 17| number=8 |publisher= American Library Association}}</ref> A CD-RW [[compact disc]] (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 (CD)|PMA]], [[TOC (CD)|TOC]] and [[pregap]], are 
not cleared. Fast blanking is quicker and usually sufficient to allow rewriting the disc. Full blanking removes all traces of the previous data,<ref>{{Cite web|last=van Hove|first=Peter |date=c. 2012 |title=Quick erased (blanked) CD-RW vs. DVD-RW vs. DVD+RW, what's recoverable and how|url=http://www.isobuster.com/tips/quick_erased_optical_discs_what_is_recoverable_and_how|url-status=live|archive-url=https://web.archive.org/web/20120924041326/http://www.isobuster.com/tips/quick_erased_optical_discs_what_is_recoverable_and_how|archive-date=2012-09-24|access-date=2020-07-19|website=IsoBuster}}</ref> 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). 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.

== CD-MO ==<!-- This section is linked from [[Curie point]] -->
Before CD-RW technology, in 1990 a standard for [[magneto-optical]] recordable and erasable CDs called CD-MO was introduced and set in the [[Rainbow Books|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. [[Dysprosium|Dy]][[Iron|Fe]][[Cobalt|Co]] or less often [[Terbium|Tb]][[Iron|Fe]][[Cobalt|Co]] or [[Gadolinium|Gd]][[Iron|Fe]][[Cobalt|Co]]) 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. Reading the discs relied on the [[magneto-optic Kerr effect|Kerr effect]] - 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,<ref name="mueller">[https://books.google.com/books?id=eV1_LjW3pTkC&pg=PA739&lpg=PA739 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"</ref> mostly because of incompatibility with standard CD reading units. Early [[CD-R]] 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.<ref>{{cite web |url=https://www.ip.philips.com/download_attachment/162/sl00272productlistCD.pdf |archive-url=https://wayback.archive-it.org/all/20080406184422/http://www.ip.philips.com/download_attachment/162/sl00272productlistCD.pdf|url-status=dead |title=Product catalogue / Pricelist: CD products |archive-date=6 April 2008|date=6 February 2012|access-date=10 April 2018}}</ref><ref>{{Cite web|url=https://git.scptuj.si/users/sign_in|title=Sign in|website=GitLab}}</ref> Other magneto-optical media, unbound by limitations of the typical CD-ROM filesystems, replaced the CD-MO.

== Mechanism of action ==<!-- Google translated from WP-de -->
Rewritable media can, with suitable hardware, be re-written up to {{nowrap|100,000 times}}<!--check if this is what the original text says!-->. The CD-RW is based on [[Phase transition|phase change]] technology, with a degree of reflection at {{nowrap|15–25%}},<ref name=gtfq/> compared to {{nowrap|40–70%}} for CD-R discs.<ref name=gtfq /> The properties of the medium and the write and erase procedure is defined in the [[Rainbow Books|Orange Book Part III]].

To maintain a precise rotation speed, tracks have a slight superimposed [[Sine wave|sinusoidal]] excursion of {{nowrap|0.3 [[Micrometre|µm]]}} at a frequency of {{val|22.05|ul=kHz}}.<ref name=gtfq/> In addition a {{val|1|u=kHz}} [[frequency modulation]] is applied to provide the recorder with an absolute time reference.<ref name=gtfq/> Groove width is {{val|0.6|ul=µm}} and pitch of {{val|1.6|u=µm}}.<ref name=gtfq/>

The media for CD-RW has the same layers as CD-R media. The reflective layer is, however, a [[silver]]-[[indium]]-[[antimony]]-[[tellurium]] ([[AgInSbTe]]) alloy with a [[polycrystal]]line structure and [[Reflection (physics)|reflective]] properties in its original state. When writing the laser beam uses its maximum power ({{nowrap|8-14 mW}})<ref name=gtfq/> to heat the material to {{nowrap|500–700 °C}} causing material [[Melting|liquefaction]]. In this state, the alloy loses its polycrystalline structure and reflectivity and assumes an [[Amorphous solid|amorphous]] state. The lost reflectivity serves the same function as bumps on manufactured CDs.<ref name=hwcd>{{cite web|url=http://computer.howstuffworks.com/cd-burner8.htm|title=How CD Burners Work|date=1 August 2001|website=howstuffworks.com|access-date=10 April 2018}}</ref> The polycrystalline state of the disc forms the trenches.<ref name=hwcd/> 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 {{nowrap|200 °C}}. The alloy is not melted, but returns to the polycrystalline state and is again reflective.

==Authoring==
[[File:CDRW PMA.jpg|thumb|right|Data structure on a CD-RW]]
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.<ref name=":0">{{Cite journal |last=Mielewczik |first=Michael |date=1999 |title=Nachschlag gefällig? Überlange CDs brennen. |journal=PC Intern |language=German |volume=3/99 |pages=118–122}}</ref>
*'''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 (CD)|TOC]] while the [[session (CD)|session]] is still open.<ref name=":0" /> PMA records may contain information on up to 99 audio tracks and their start and stop times ([[CD-DA]]), 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==
{| class="wikitable" style="float:right; margin-left: 1em;"
!Specification<ref>{{Cite web|url=http://www.cdrfaq.org/faq04.html|title = CD-Recordable FAQ - section 4}}</ref>
!Logo
!Speed
|-
|(Original, "slow")
|[[File:CDRW-Logo.svg|50px]]
|1×, 2×, 4×
|-
|High Speed
|[[File:CDHSRW.svg|50px]]
|8×, 10×, 12×
|-
|Ultra Speed
|[[File:CDRW UltraSpeed-Logo.svg|50px]]
|16×, 20×, 24×
|-
|Ultra Speed+
|[[File:CDRW UltraSpeed-Plus-Logo.svg|50px]]
|32×
|}
[[File:CDHSRW.svg|thumb|100px|Philips created the "High-Speed" CD-RW logo for media that supports writing speeds above 4×.]]

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]] 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.{{cn|date=May 2022}}

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.

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.{{Citation needed|date=July 2010}}

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 Corporation|Pioneer]] ''DVR-110D'' (2005),<ref name=DVR-110D>{{Cite web|url=https://www.pioneerelectronics.com/PUSA/Computer/Computer+Drives/DVR-110D|title=DVR-110D - Internal DVD/CD writer for desktop computer|website=Pioneer Electronics USA}}</ref> [[Hitachi-LG Data Storage|Hitachi-LG]] ''GSA-4167'' (2005)<ref>{{Cite web|date=2005|title=GSA-4167B Super Multi DVD Drive – Owner's Manual|url=http://gscs-b2c.lge.com/downloadFile?fileId=KROWM000097258.pdf|url-status=live|archive-url=https://web.archive.org/web/20200809025505/http://gscs-b2c.lge.com/downloadFile?fileId=KROWM000097258.pdf|archive-date=2020-08-09|access-date=2020-08-09|publisher=[[Hitachi-LG Data Storage]]}}</ref>'',''  TSSTcorp ''SH-S182/S183'' (2006) and ''SH-S203/TS-H653B'' (2007) have officially adapted support for CD-RW ''UltraSpeed Plus'' (32× [[Z-CLV]]), while more recent DVD writers such as the ''SH-224DB'' (2013) and Blu-Ray writers such as the ''[[Hitachi-LG Data Storage|LG]] BE16NU50'' (2016) have downgraded the [[backwards compatibility]] to CD-RW ''UltraSpeed'' (24× Z-CLV).<ref name=HL-DT-ST-Discontinued>{{Cite web|url=https://www.lg.com/us/burners-drives/discontinued|title=archive.ph|website=archive.today|access-date=2020-07-20|archive-date=2020-07-11|archive-url=https://archive.today/20200711193519/https://www.lg.com/us/burners-drives/discontinued|url-status=bot: unknown}}</ref><ref name=TSST-Manuals>{{Cite web|url=http://www.tsstodd.com/manual-2/|title=Manual}}</ref>

''[[Optical disc drive#Form factors|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×<ref>{{cite web |title=Apple USB SuperDrive |url=https://www.apple.com/shop/product/MD564LL/A/apple-usb-superdrive |website=Apple |publisher=[[Apple Inc.]]}}</ref><ref>{{cite web |title=Apple USB SuperDrive - DVD±RW (±R DL) drive - Hi-Speed USB Series Specs |url=https://www.cnet.com/products/apple-usb-superdrive-dvdrw-r-dl-drive-hi-speed-usb-series/#:~:text=specs%201%20Speeds%208x%2F8x%202%20Read%20Speed%2024x,DL%2C%20DVD%2BRW%2C%20DVD-ROM%207%20Media%20Load%20Type%20slot-load |website=CNET |publisher=[[CNet]] |language=en |quote=Rewrite Speed: 16x (CD)}}</ref><ref name=BU20>[https://www.lg.com/us/support/products/documents/LG_SPEC_BU20N_041532_PR.pdf 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.<ref name=HL-DT-ST-Discontinued/><ref name=TSST-Manuals/><ref name=eTAU108>[https://www.cnet.com/products/liteon-etau108-dvdrw-r-dl-dvd-ram-drive-hi-speed-usb-series/ LiteOn eTAU108 - DVD±RW (±R DL) / DVD-RAM drive - Hi-Speed USB Series Specification sheet and picture] - CNet.com, 2009; accessed July 11th 2020.</ref><ref>{{cite web |title=Downloads {{!}} eBAU108 Manual {{!}} External Slim DVD-RW {{!}} Manual |url=http://www.liteonodd.com/en/service-support/download/cat_view/42--manual/90-external-slim-dvd-rw/121-ebau108-manual.html |website=www.liteonodd.com |publisher=[[Lite-On]] |archive-url=https://web.archive.org/web/20150310014049/http://www.liteonodd.com/en/service-support/download/cat_view/42--manual/90-external-slim-dvd-rw/121-ebau108-manual.html |archive-date=2015-03-10 |url-status=dead}}</ref>

== See also ==
* [[List of optical disc manufacturers]]

== References ==
{{Reflist |refs=

<ref name=gtfq>{{Cite web |url=http://home1.gte.net/johnfull/n235.htm |title=Frequently asked questions about hardware |access-date=2011-05-15 |archive-url=https://archive.today/20120709220909/http://home1.gte.net/johnfull/n235.htm |archive-date=2012-07-09 |url-status=dead |quote=CD Recordable and CD ReWriteable discs have the same basic structure but with significant detailed differences. The CD-R has a dye based recording layer, with a reflectivity of 40-70 %, while the CD-RW has a phase change recording layer with a reflectivity of 15-25 %. Both have an additional reflecting layer (gold) for the CD-R and (silver) for the CD-RW.}}</ref>

}}
{{Refbegin}}
* 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 [[Klara Nahrstedt|Nahrstedt, Klara]]. "Multimedia Fundamentals Volume 1: Media Coding and Content Processing", {{ISBN|0-13-031399-8}}.
{{Refend}}

== External links ==
* [http://www.ecma-international.org/publications/standards/Ecma-395.htm ECMA-395: Recordable Compact Disc Systems CD-RW Ultra-Speed] (standardized Orange Book, Part III, Volume 3)
* [http://www.cdrfaq.org/ The CD-R FAQ]
* [http://www.osta.org/technology/pdf/cdr_cdrw.pdf http://www.osta.org/technology/pdf/cdr_cdrw.pdf]
* [http://www.osta.org/technology/cdqa.htm Understanding CD-R & CD-RW]
* [http://www.pctechguide.com/33CDR-RW_CD-RW.htm PC Technology Guide] {{Webarchive|url=https://web.archive.org/web/20090330222151/http://www.pctechguide.com/33CDR-RW_CD-RW.htm |date=2009-03-30 }}

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