Some of the CD-R’s that I burnt way back in 2002 are now suffering from data rot. They are just not readable anymore and it looks like their recording surface has faded. However CD-ROMs that I had received thru books/magazines that too way back in 1998/99 time frame are still intact and working fine.

That makes me wonder if pressed ROM disks have longer life than recordable burnt ones. Is there any scientific or technical explanation that exists or is it just a matter of luck in my case?



Pressed disks do have a longer life. There's great variation in manufacturing and materials quality. There are also different types of material used for the reflective layer within each type of disk, and these vary in longevity. So it's dangerous to make blanket statements by media type. You can find high quality and crap in every media type. However, comparing media of similar quality, recordable disks have a shorter service life and are also more susceptible to degradation.

Different types of optical disks use different material for the data layer. ROM disks have the data pressed into the reflective layer. Recordable disks have a reflective layer plus another layer that holds the data. The data layer on recordable disks typically degrades and fails before the reflective layer.

R discs use an organic dye-based layer for recording data. The organic dye used in the data layer of R discs degrades naturally but slowly over time. High temperatures and humidity will accelerate the process. Prolonged exposure to UV light can degrade the dye properties and eventually make the data unreadable. Heat buildup within the disc, caused by sunlight or close proximity to heated light sources, will also accelerate dye degradation.

RW discs are generally not considered for long-term or archival use, and life expectancy tests are seldom done for this medium. Rewritable discs use a phase-changing metal alloy film for recording data. The alloy film is not as stable as the dye used in R discs because the material normally degrades at a faster rate.

The phase-changing film is affected primarily by heat, but ultraviolet (UV) light may also be a factor in the aging process. The combination of high temperature and UV light may further accelerate the aging process. The combination of high temperatures and high relative humidity will also most likely accelerate the aging process, just as it does with the organic dye used in R discs.

The data on the phase-changing metal alloy film layer can be erased and rewritten to a limited number of times. This rewriting affects disc life expectancy; RW discs archived after the first recording should have a longer life expectancy than those that have undergone several erase-recording cycles. Given the normal degradation rate alone, the life expectancy for RW discs will be less than that of R discs. Add to that multiple rewrites, and the life expectancy can be even less.

excerpted from https://www.clir.org/pubs/reports/pub121/sec4.html

Additional reading: https://en.wikipedia.org/wiki/Disc_rot

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