CD-R

A CD-R (Compact Disk - Recordable) is a thin (1.2 mm) disc made of polycarbonate with a 120 mm diameter that is mainly used to store music or data. However, unlike conventional CD media, a CD-R has a core of dye instead of metal.

A CD-R has usually a storage capacity of 650 MB or 700 MB.

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 a special dye and subequently 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-irradiation.

A specially designed type of CD-ROM drive, called a CD-R drive, CD burner, or CD writer can be used to write CD-Rs. A laser is used to etch ("burn") small pits into the dye so that the disc can later be read by the laser in a CD-ROM drive or CD player. The laser used to write CD-Rs is a infrared laser which emits laser radiation at a wavelength of 780 nm. The reflectivity in the pit area is different (lower) than for the unchanged dye area, because the refractive index of the dye is lowered upon "burning" a pit. Upon reading back the stored information, the laser operates at a low enough power not to "burn" the dye and an optical pick-up records the changes in the intensity of the reflected laser radiation when scanning along the groove and over the pits. The change of the intensity of the reflected laser radiation is transformed into an electrical signal, from which the digital information is recovered ("decoded"). The decomposition of the dye in the pit area through the heat of the laser is irreversible (permanent). Therefore, once a section of a CD-R is written, it cannot be erased or rewritten, unlike a CD-RW. A CD-R can be recorded in multiple sessions.

The CD-R was invented in 1988 by the Japanese company Taiyo Yuden. First CD-Rs were produced in 1994. Among the first manufacturers were the companies Taiyo Yuden, Kodak, Memorex, Maxell, and TDK. Since then, the CD-R was further improved to allow writing speeds as fast as 52x and even 54x relative to the first 1x CD-Rs. The improvements were mainly due to optimisation of special dye compositions for CD-R, groove geometry, and the dye coating process. Low-speed burning at 1x is still used for special "audio CD-Rs", since CD-R audio recorders got standardized to this recording speed.

Early dyes used for CD-R were cyanine dyes. These dyes were later more and more replaced by azo dyes and predominantly phthalocyanine dyes, which are better suited to a wide range of recording speeds and are more stable than cyanine dyes.

Although the CD-R was initially developed in Japan, most of the production of CD-R had moved to Taiwan since 1998. Taiwanese manufacturers supplied more than 70% of the worldwide production volume of 10.5 bn CD-Rs in 2003.

There was some incompatibility with CD-Rs and older CD-ROM drives. This was primarily due to the lower reflectivity of the CD-R disc. In general, CD drives marked as 8x or greater will read CD-R discs. Some DVD players will not read CD-Rs because of this change in reflectivity as well.

see also: CD-ROM, DVD, DVD-R, DVD plus R, CD burner, Spindle

External links

• The CD-R FAQ: http://www.cdrfaq.org/