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How many times can a CD-RW disc be rewritten?
As is the case with all optical storage media using phase change technology there is a limit to the number of times the recording layer in a CD-RW disc can be reliably switched between its crystalline and amorphous states. Currently, CD-RW discs can be rewritten approximately 1000 times.
What is the shelf life of unrecorded CD-R and CD-RW discs?
The unrecorded shelf life of a CD-R or CD-RW disc is conservatively estimated to be between 5 and 10 years.
How long will data recorded on CD-R and CD-RW discs remain readable?
The life span of a written disc depends upon a number of factors including such things as the intrinsic properties of the materials used in the disc’s construction, its manufactured quality, how well it is recorded and its physical handing and storage. As a result, the life span of a recorded disc is extremely difficult to estimate reliably. However, to calculate disc life spans within some practical timeframe blank media manufacturers do conduct accelerated age testing by subjecting samples of their discs to environments much beyond those experienced under normal storage conditions. Generally speaking, only the effects of varying temperature and humidity are considered. These test results are then used to predict how long a disc will remain readable under more normal storage conditions. Since questionable testing and measurement procedures can seriously impact upon and compromise these estimates several international standards have been developed which specify procedures to be used conducting accelerated testing and analyzing the resulting data from prerecorded (pressed) and recordable CDs:
ISO 18921:2002, Imaging materials — Compact discs (CD-ROM) — method for estimating the life expectancy based on the effects of temperature and relative humidity
ISO 18927:2002, Imaging materials — Recordable compact disc systems — method for estimating the life expectancy based on the effects of temperature and relative humidity
For years now many media manufacturers have performed their own lifetime evaluations using these or a variety of other homegrown tests and mathematical modeling techniques. Historically, manufacturers have claimed life-spans ranging from 50 to 200 years for CD-R discs and 20 to 100 years for CD-RW. Be aware, however, that disc producers, manufacturing methods and materials change over time as do applications and cost imperatives. Consequently, those concerned with disc longevity should consult the appropriate international standards and their media manufacturer for more particular information.
It is important to remember, however, that nothing lasts forever and that technologies inevitably change. Well-designed products, such as CD-R and CD-RW, allow for seamless transition to the next generation and ultimately, since they embody digital information, contents can be transferred to future storage systems as becomes necessary to preserve whatever has been stored on the discs.