Optical discs can be convenient media for access and temporary storage. Unfortunately, such media are machine-dependent, so access is contingent on surviving and working hardware and software. Additionally, such media is subject to changing manufacturer standards, as well as deterioration, just like any other material.
Optical discs are made of many layers, and the materials used in these layers change over time, depending on how and when the discs were made and how they age. Depending on susceptibility, wear, and environment, various layers of optical discs may undergo oxidation, hydrolysis or mechanical stress, leading to damage (variously described as “rot” or “pin holes” or “mirroring”, etc.). These and other phenomenon may lead to errors in signal playback, which can be assessed by measuring a disc’s “block error rate” or BLER. The greater the BLER, the greater the loss of information.
The Information Access Division of the National Institute of Standards and Technology (NIST) and the Preservation Directorate at the Library of Congress agreed to perform a detailed investigation of the longevity of recordable Compact Disc (CD) and Digital Versatile Disc (DVD) media. The effort was aimed at estimating the life expectancy of information stored in CD-R, DVD-R and DVD+R, as well as DVD-RW and DVD+RW discs.
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