Life Expectancy CD-ROM and DVD-ROM's We are offering this advice as a guide only, these are not the absolute guidelines for storing your CD-R and DVD-R's. Please check with your governing agency as to your specific needs. The life expectancy (LE) of optical discs depends on many factors, some controllable by the user, others not. The two basic types of CD and DVD discs we use are CD-ROM and DVD-ROM. These use a different data layer material (molded aluminum, organic dye, or phase-changing film, respectively). Deterioration of this material is the primary cause for disc degradation and, ultimately, "end of life" for the disc, assuming proper physical handling. Environmental factors can affect the rate of disc degradation. 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). 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. Physical mishandling of the disc is usually the cause of polycarbonate layer damage. The polycarbonate may also flex or bend if stored for a long period of time in a non vertical position. So what is the life expectancy of a disc? First, we must define life expectancy. For most users, it means the length of time for which the disc remains usable. But that implies some acceptable amount of degradation. How much and what type of degradation is acceptable? 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. The user notices a problem only when the error correction coding is unable to fully correct the errors. 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 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. 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. Manufacturers tend to use this premise to estimate media longevity. They test discs by using accelerated aging methodologies with controlled extreme temperature and humidity influences over a relatively short period of time. However, it is not always clear how a manufacturer interprets its measurements for determining a disc's end of life. Among the manufacturers that have done testing, there is consensus that, under recommended storage conditions, CD-R and DVD-R should have a life expectancy of 100 to 200 years or more. Little information is available for CD-RW and DVD-RW discs (including audio and video), resulting in an increased level of uncertainty for their life expectancy. Expectations vary from 20 to 100 years for these discs. Few, if any, life expectancy reports for these discs have been published by independent laboratories. An accelerated aging study at NIST (National Institute of Standards and Technology) estimated the life expectancy of one type of CD-R and DVD-R for authoring disc to be 30 years if stored at 25°C (77°F) and 50% relative humidity. This testing for R discs is in the preliminary stages, and much more needs to be done. Another very important variable to be considered concerns technology migration. The number one unavoidable fact is that electronically stored records are technology dependent and therefore technology obsolescence is likely to be the most serious impediment to the long-term usability of these records. Therefore, the development and implementation of a migration strategy to ensure that digital records created today can be both processed by computers and intelligible to humans in the 21st century is absolutely essential. Imagine if your data were on 8 track tapes, where can one find an 8 track tape player these days? Or how about this argument; how many of you still have a 5 1/4 inch floppy drive to read those big floppy discs? I bet if you dig deep enough somewhere back in your companies archive you would find some of those now ancient (it's been less than 15 years) 5 1/4 floppies and you would probably find that your current IT department has no way of reading these discs either. <> Back to Top <> Contact Us__|__Send e-mail__|__Site Index__|__Home Page