Disc Longevity

How many times can a DVD-RW, DVD+RW and DVD-RAM disc be rewritten?
As is the case with other optical storage media using phase-change technology there is a limit to the number of times the recording layer in a DVD-RW, DVD+RW and DVD-RAM disc can be reliably switched between its crystalline and amorphous states. It is estimated that a DVD-RW or DVD+RW disc can be rewritten approximately 1000 times and a DVD-RAM 100,000 times. In addition, these formats (under certain circumstances) employ defect management schemes to actively verify data and skip over or relocate problems to a spare area of the disc.

How long will data recorded on writable DVD 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, the quality of its manufacture, how well it is recorded and the way it has been handled and stored. 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 conduct accelerated age testing by subjecting samples of their discs to environments much beyond those experienced under normal storage conditions. Generally speaking, these tests only consider the effects of varying temperature and humidity. Results are then used to predict how long a disc will remain readable under more normal storage conditions. Questionable testing and measurement procedures can seriously impact upon and compromise these estimates so keep in mind that unlike prerecorded (pressed) CD and CD-R discs there are currently no international standards for conducting writable DVD accelerated testing. Writable DVDs and CDs may appear similar, but their construction and underlying design differ significantly so what applies to the one does not necessarily apply to the other.

As with CD-R and CD-RW discs media manufacturers have performed their own lifetime evaluations using a variety of homegrown tests and mathematical modeling techniques. Generally speaking, manufacturers claim life spans ranging from 30 to 100 years for DVD-R and DVD+R discs and up to 30 years for DVD-RW, DVD+RW and DVD-RAM. 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 their media manufacturer for more particular information.

One thing is sure — nothing lasts forever and technologies inevitably change. Ultimately, since writable DVDs embody digital information, contents may be transferred to future storage systems as becomes necessary to preserve whatever has been stored on the discs.

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