Subject: [7-5] How long do CD-Rs and CD-RWs last?
(2005/04/14)
CD-RWs are expected to last about 25 years under ideal conditions (i.e. you write it once and then leave it alone). Repeated rewrites will accelerate this. In general, CD-RW media isn't recommended for long-term backups or archives of valuable data.
The rest of this section applies to CD-R.
The manufacturers claim 75 years (cyanine dye, used in "green" discs), 100 years (phthalocyanine dye, used in "gold" discs), or even 200 years ("advanced" phthalocyanine dye, used in "platinum" discs) once the disc has been written.
The shelf life of an unrecorded disc has been estimated at between 5 and 10 years. There is no standard agreed-upon way to test discs for lifetime viability. Accelerated aging tests have been done, but they may not provide a meaningful analogue to real-world aging.
Exposing the disc to excessive heat, humidity, or to direct sunlight will greatly reduce the lifetime. In general, CD-Rs are far less tolerant of environmental conditions than pressed CDs, and should be treated with greater care. The easiest way to make a CD-R unusable is to scratch the top surface. Find a CD-R you don't want anymore, and try to scratch the top (label side) with your fingernail, a ballpoint pen, a paper clip, and anything else you have handy. The results may surprise you.
Keep them in a cool, dark, dry place, and they will probably live longer than you do (emphasis on "probably"). Some newsgroup reports have complained of discs becoming unreadable in as little as three years, but without knowing how the discs were handled and stored such anecdotes are useless. Try to keep a little perspective on the situation: a disc that degrades very little over 100 years is useless if it can't be read in your CD-ROM drive today.
One user reported that very inexpensive CD-Rs deteriorated in a mere six weeks, despite careful storage. Some discs are better than others.
An interesting article by Fred Langa (of
http://www.langa.com/) on
http://www.informationweek.com/story/sh ... 263&pgno=1 describes how to detect bad discs, and discusses whether putting an adhesive label on the disc causes them to fail more quickly.
By some estimates, pressed CD-ROMs may only last for 10 to 25 years, because the aluminum reflective layer starts to corrode after a while.
One user was told by Blaupunkt that CD-R discs shouldn't be left in car CD players, because if it gets too hot in the car the CD-R will emit a gas that can blind the laser optics. However, CD-Rs are constructed much the same way and with mostly the same materials as pressed CDs, and the temperatures required to cause such an emission from the materials that are exposed would melt much of the car's interior. The dye layer is sealed into the disc, and should not present any danger to drive optics even if overheated. Even so, leaving a CD-R in a hot car isn't good for the disc, and will probably shorten its useful life.
See also
http://www.cd-info.com/CDIC/Technology/ ... evity.html, especially
http://www.cd-info.com/CDIC/Industry/ne ... ology.html about some inaccurate reporting in the news media.
See "Do gold CD-R discs have better longevity than green discs?" on
http://www.mscience.com/faq53.html.
There's a very readable discussion of CD-R media error testing on
http://web.archive.org/web/200312111517 ... na296.html that leaves you with a numb sense of amazement that CD-Rs work at all. It also explains the errors that come out of MSCDEX and what the dreaded E32 error means to a CD stamper.
An interesting document entitled "Care and Handling of CDs and DVDs - A Guide for Librarians and Archivists" can be found on the web sites for the National Institute of Standards and Technology (NIST) and the Council on Library and Information Resources (CLIR). View it on the web at
http://www.clir.org/pubs/reports/pub121/contents.html or as a PDF from
http://www.itl.nist.gov/div895/careford ... gGuide.pdf. It has a wealth of information about disc composition and longevity, as well as recommendations for extending the lifespan of your media.
Another good NIST article, "Stability Comparison of Recordable Optical Discs -- A Study of Error Rates in Harsh Conditions" can be found at
http://www.itl.nist.gov/div895/gipwg/StabilityStudy.pdf.
http://www.cdrfaq.org/faq07.html
Kodak has some interesting information about their "Ultima" media. See
http://www.kodak.com/global/en/service/ ... ndex.jhtml, specifically the "KODAK Ultima Lifetime Discussion" and "KODAK Ultima Lifetime Calculation" white papers (currently in PDF format). The last page discusses the Arrhenius equation, which is used in chemistry to calculate the effect of temperature on reaction rates. The Kodak page defines it as:
t = A * exp(E/kT)
where 'exp()' indicates exponentiation. 't' is disc lifetime, 'A' is a time constant, 'E' is activation energy, 'k' is Boltzmann's constant, and 'T' is absolute temperature. The equation allows lifetime determined at one temperature to be used to establish the lifetime at another. If a disc breaks down in three months in extreme heat, you can extrapolate the lifetime at room temperature.
The trouble with the equation is that you have to know either 'A' or 'E'. It appears that 'A' can be estimated based on empirical evidence, but see
http://palimpsest.stanford.edu/byorg/ab ... 3-308.html for some cautions about how tricky it can be to choose the right value.
