![]() ![]() Little information is available for CD-ROM and DVD-ROM discs (including audio and video), resulting in an increased level of uncertainty for their life expectancy. Among the manufacturers that have done testing, there is consensus that, under recommended storage conditions, CD-R, DVD-R, and DVD+R discs should have a life expectancy of 100 to 200 years or more CD-RW, DVD-RW, DVD+RW, and DVD-RAM discs should have a life expectancy of 25 years or more. However, it is not always clear how a manufacturer interprets its measurements for determining a disc’s end of life. They test discs by using accelerated aging methodologies with controlled extreme temperature and humidity influences over a relatively short period of time. Manufacturers tend to use this premise to estimate media longevity. When the number of errors (before error correction) on a disc increases to a certain level, the chance of disc failure, even if small, can be deemed unacceptable and thus signal the disc’s end of life. The chance of disc failure increases with the number of errors, but it is impossible to define the number of errors in a disc that will absolutely cause a performance problem (minor or catastrophic) because it depends on the number of errors left, after error correction, and their distribution within the data. One method for determining end of life for a disc is based on the number of errors on a disc before the error correction occurs. The user notices a problem only when the error correction coding is unable to fully correct the errors. With CDs and DVDs, the user does not notice early degradation because the error detection and correction capability built into the system corrects a certain number of errors. ![]() How much and what type of degradation is acceptable? But that implies some acceptable amount of degradation. For most users, it means the length of time for which the disc remains usable. So what is the life expectancy of a disc? First, we must define life expectancy. The polycarbonate may also flex or bend if stored for a long period of time in a nonvertical position. Physical mishandling of the disc is usually the cause of polycarbonate layer damage. Because degradation of the data layer will render the disc useless well before the polycarbonate begins to deteriorate, the relative degradation rate for the polycarbonate layer is not used for life expectancy considerations. In each of the three basic disc types, environmental forces will degrade the data layer much faster than the polycarbonate substrate layer (the clear plastic that makes up most of the disc). Deterioration of this material is the primary cause for disc degradation and, ultimately, “end of life” for the disc, assuming proper physical handling.Įnvironmental factors can affect the rate of disc degradation. ![]() The life expectancy (LE) of optical discs depends on many factors, some controllable by the user, others not.įactors that affect disc life expectancy include the following:Īs noted previously, the three basic types of CD and DVD discs-ROM, R, and RW and RAM-each use a different data layer material (molded aluminum, organic dye, or phase-changing film, respectively). ![]()
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