Storage: Do burned CDs and DVDs have a shelf life?

About CD/DVD Lifespans

In reply to: Do burned CDs and DVDs have a shelf life? by Lee Koo (ADMIN) 

Data Rot or Bit Rot are the terms used to describe this. In a way these are misleading as data itself has no physical properties to rot. However, the physical media data is stored upon can do exactly that - rot. It only takes a tiny degree of physical degradation, usually quite invisible to the human eye, to affect data. Older storage media such as floppy disks and magnetic tape were more prone to "rot" phenomena as they could also lose their magnetic alignment over time.

CDs and DVDs made of high quality material have little to no ability to "rot" but the usual lower end disks often can and do lose data over time. CDs can lose their reflective coating over time and thus become useless. This type of "rot" is called "bronzing" and is one that is visible to the human eye. The disks gradually turn brownish in color usually beginning at the outer edge of the cd and spreading toward the center almost like a fungus. This problem, thankfully, is not as common today as it was in the 1990s although older disks from that time period may yet become "bronzed" so if you have any, it would be a very good idea to make copies on newer disks.

CDs can lose their reflective coating in other ways too - oxydation, scratches, even melting in a hot car. A DVD on the other hand has an extra layer of plastic atop the reflective section thus is less prone to problems of this type. They are not without their own issues though. Many DVDs have proven to be prone to a problem called "delamination" which is oddly similar to the older "bronzing" problem of CDs. You can read more about the physical structure of CDs and DVDs and their similarities and differences at http://computer.howstuffworks.com/cd1.htm and http://electronics.howstuffworks.com/dvd.htm. Also, it is worth mentioning that CD-RW disks are quicker to degrade than non-rewriteable disks. Their material is easier to melt or become otherwise unreadable than the material used to make non-rewriteable disks.

The general consensus for extending CD and DVD life often comes down to how they are stored. It seems most claim that CDs and DVDs should be stored in jewel cases for optimum "shelf life". This allows the recordable surfaces of the disks to remain effectively untouched while stored. Paper jackets, envelopes, and CD binders are considered to be not so good as the disk surface is continually in contact with the storage device. However, such methods of storage for CDs and DVDs are considered better than no protection at all.

In verifying my facts for this response, I ran across something else I'd not seen before which seems worth mentioning here - Apparently some claim that specific data formats have better archival abilities than do others. The article states that the file type used can indeed matter and claims that the more stable formats are: ASCII text, PDF, RTF, PNG, TIFF, JPEG, MP3, WSAV, AIFF, MPEG, and DBF. It lists as unstable formats DOC, GIF, BMP, AU, WMV, RA, AVI, MOV, and all Excel and MS Access file formats. I believe they were also adding in to their measures of stability the likelihood of such formats being able to be read by tomorrows devices but this is something that bears looking into further. I found this blurb within a rather long document at: http://www.slais.ubc.ca/PEOPLE/students/student-projects/C_Hill/hill_libr516/print.htm - it is listed within the document under the heading of "The Future".

Wikipedia has a good article on CDs that includes much information on the various types of dyes used to produce the coating on CDs. Apparently the type of dye used directly affects the "shelf life" of a CD. This article can be found at: http://en.wikipedia.org/wiki/CD-R The same article itself echoes what seems to be most often written - that lower end CDs tend to have a useful life of anywhere from one to five years but that higher end CDs effectively have no specific limit to their lifespans as yet. Some manufacturers are claiming archival life of as much as 300 years with the more common claim being 100 years for archival quality CDs. MAM-A (http://www.mam-a.com/) claims a 300 year shelf life for their Gold Archive CD disks and a 100 year shelf life for their Archive Grade DVDs. Other brands known for longevity are Taiyo Yuden, Ricoh, TDK, and Verbatim. A caution here though - most of these manufacturers also make low end disks so be sure the disks you are buying state that they are archival quality.

I will end here before I write a book but want to mention one more thing: As with any and everything, if it matters to you, back it up, back it up, and back it up again! Anything important should have at least 3 copies with at least one stored in a separate location in case of disaster. To avoid the issue of degradation as much as possible, it is not at all a bad idea to take a day or two each year and re-backup your backups. In other words, copy all your archives to yet another, new CD or DVD. Copy your oldest copies each year and the degradation issue should not be a problem at all. If this is Just Too Much to do then you might also want to copy your CDs and DVDs onto an external hard drive or two and at least re-copy that every year. This of course would be an easier and less time consuming process as theoretically you could set the copy process in motion and leave it alone til done whereas with disks you need to be present to continually change them out.

Happy copying!