Blank CDs

A CD-R (Compact Disc-Recordable) is a variation of the Compact Disc invented by Philips and Sony. more...

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CD-R is a Write Once, Read Many optical media (though the whole disk does not have to be entirely written in the same session) and retains a high level of compatibility with standard CD readers (unlike CD-RW which can be rewritten but has much lower compatibility and the discs are considerably more expensive).

History

The CD-R, originally named CD Write-Once (WO), specification was first published in 1988 by Philips and Sony in the 'Orange Book'. The Orange Book consists of several parts, furnishing details of the CD-WO, CD-MO (Magneto-Optic), and CD-RW (ReWritable). The latest editions have abandoned the use of the term "CD-WO" in favor of "CD-R", while "CD-MO" were practically never used. Written CD-Rs and CD-RWs are fully compatible with the Audio CD (Red Book) and CD-ROM (Yellow Book) standards. They use Eight-to-Fourteen Modulation, CIRC error correction plus the third error correction layer defined for CD-ROM.

The dye materials developed by Taiyo Yuden made it possible for CD-R discs to be compatible with Audio CD and CD-ROM discs.

Physical characteristics

A standard CD-R is a 1.2 mm thick disc made of polycarbonate with a 120 mm or 80 mm diameter. It has a storage capacity of 74 minutes of audio or 650 MiB of data. CD-R/RWs are also available with capacities of 79 minutes, 59 seconds and 74 frames (marketed as 80 minutes) /736,966,656 bytes (702 MiB), which they achieve by burning at the maximum allowable tolerances specified in the Orange Book CD-R/CD-RW standards. Most CD-Rs on the market have an 80 minute capacity. There are also 90 minute/790 MiB and 99 minute/870 MiB discs, although they are rare. Some drives use special techniques to write more data onto a given disc, such as Plextor's GigaRec allowing as much as 1.2 GiB onto a 99 minute disc. Also, due to the limitations of the data structures in the ATIP (see below), 90 and 99 minute blanks will identify as 80 minute ones and have to be burned using the "overburn" options in the CD recording software.

The polycarbonate disc contains a spiral groove to guide the laser beam upon writing and reading information. The disc is coated on the side with the spiral groove with a very thin layer of organic dye and subsequently with a thin, reflecting layer of silver, a silver alloy or gold. Finally, a protective coating of a photo-polymerizable lacquer is applied on top of the metal reflector and cured with UV-light.

A blank CD-R is not "empty", it has a pregroove with a wobble (the ATIP), which helps the writing laser stay on track and is used to ensure the data is written to the disc at a constant rate. As well as providing timing information, the ATIP (absolute time in pregroove) is also a data track containing information about the CD-R manufacturer, the dye used and media information (disc length etc). The pregroove is not destroyed when the data is written to the CD-R, a point which some copy protection schemes use to distinguish copies from an original CD.

Read more at Wikipedia.org