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.
CONTINUE TO DISC TESTING