CD-R – Recordable Compact Disk

Write Once/Read Many storage (WORM) has been around since the late 1980s, and is a type of optical drive that can be written to and read from. When data is written to a WORM drive, physical marks are made on the media surface by a low-powered laser and since these marks are permanent, they cannot be erased, hence write once. The characteristics of a recordable CD were specified in the Orange Book II standard in 1990 and Philips was first to market with a CD-R product in mid-1993. It uses the same technology as WORM, changing the reflectivity of the organic dye layer which replaces the sheet of reflective aluminium in a normal CD disc. In its early days, cyanine dye and its metal-stabilised derivatives were the de facto standard for CD-R media. Indeed, the Orange Book, Part II, referred to the recording characteristics of cyanine-based dyes in establishing CD-Recordable standards. Phthalocyanine dye is a newer dye that appears to be less sensitive to degradation from ordinary light such as ultraviolet (UV), fluorescence and sunshine. Azo dye has been used in other optical recording media and is now also being used in CD-R. These dyes are photosensitive organic compounds, similar to those used in making photographs. The media manufacturers use these different dyes in combination with dye thickness, reflectivity thickness and material and groove structure to fine tune their recording characteristics for a wide range of recording speeds, recording power and media longevity. To recreate some of the properties of the aluminium used in standard CDs and to protect the dye, a microscopic reflective layer – either a proprietary...

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