Compact Disc-Recordable (CD-R) is an optical disc format designed by Philips and Sony, and based on the Compact Disc. CD recorders became available in 1992 but were extremely expensive and it wasn’t until 1995 that they fell below $1000 (around £650).
CD-R discs can be used for audio or data recording, but only CD-R Audio discs can be used in standalone consumer audio recorders.
CD-Rs are a Write Once Read Many (WORM) medium, although the whole disk does not have to entirely written in the same session. Their specification is taken from the Orange Book standards. Properly written CD-Rs are fully compatible with audio (CD-DA) and data (CD-ROM) Compact Disc standards.
Standard CD-Rs are 120mm in diameter (although 8cm Mini CD-Rs are also available), and most can store 74 minutes of audio or 650 MB of data. Some CD-Rs have an 80 minute or 700 MB capacity, but anything over this means they are not fully compatible with CD standards.
A CD recorder writes data to a CD-R disc by pulsing its laser to heat areas of the organic dye layer. The writing process does not produce indentations (pits) – instead, the heat permanently changes the optical properties of the dye, changing the reflectivity of those areas. Various dyes have been used over the years, with cyanine being the earliest and less stable.
In general CD-Rs are expected to have an average life expectancy of 10 years. As well as degradation of the dye, failure of a CD-R can be due to the reflective surface. While silver is more widely used, it is more prone to oxidation. Gold-based CD-Rs do not suffer from this problem, but are more expensive.