Question to the Storage Advisors, from Ned Hune: In the late 90’s there was a firestorm of controversy surrounding the lifespan of CDs (to which Tom recently alluded). Is there a definitive answer? Is it safe to use CD-Rs as a permanent archive?

I was surprised to get so much mail on the topic of CD lifespan. My original post was mostly a summarization of an interview with Kurt Gerecke of IBM/Germany. Since then I’ve had several mails, such as the one above from Ned Hune, questioning whether CD-R lifespans were still as poor as originally reported, how DVDs were affected, etc.

So I did a little additional research hoping to find a definitely answer. Unfortunately I came up dry. I did find lots of “facts” about CDs that I suppose, to a person smarter than I, would add up to a real answer. Many of these facts seem to be repeated verbatim on various blogs and message boards, and I tried to therefore to take those facts with a grain of salt. It was very difficult to find original and unique content, but I did run across the Optical Storage Technology Association website. Honestly, I couldn’t discern whether this was a legit organization, or just a group of vendors trying to sell more CD media, but they did seem to have a lot of genuine and useful information.

Also, regarding DVDs, it seems that all the information I found regarding CDs also applies to DVDs. DVD-Rs haven’t been shipping long enough to start noticing multi-year trends in reliability.

I’m going to take a crack at outlining some of the information I found, but I’ll shamefully pawn the final decision on to my fine, fine readers.

There are four major components of a CD that can suffer from degradation and thereby loss of data. The first is the organic dye that actually holds the 0’s and 1’s. Besides its natural degradation over long periods of time, this dye is mostly affected by UV (sunlight) and heat.

The second component is the polycarbonate layer. This is the clear material that makes up most of the CD. This layer can also degrade over time, becoming less and less transparent. Again, UV and heat can speed up this process, as well as acid from your hands.

The third component is the reflective layer. The best material for this layer is gold, but that adds a lot of cost. Sony sells a gold disk that they claim has a lifespan of 100-200 years. Silver or silver alloys can also be used, but they will corrode due to sulfur dioxide, i.e., air pollution. The key is keeping this layer sufficiently sealed to avoid corrosion.

The last component is the side where the label resides. This side suffers from two problems. The first is that a scratch on this side will damage the reflective layer. The second is that the glue from a paper label can corrode the disc.

So those were all reasons why a CD would degrade over the years. And hopefully you derived some tips on how to avoid, or at least slow down, the degradation. Supposedly pressed CDs, i.e., pre-recorded CDs, are better sealed, have better label glue, better reflective layers, etc., and will last longer. I could find no clear answers or guesses as to how much longer. Also, most of the vendors sell higher-end recordable CDs that claim more resistance to degradation, but again, I couldn’t find a study that conclusively proved they were better. I did find plenty of anecdotal information from users that cheaper CDs were less reliable.

It seem generally accepted that the lifespan of a CD-RW is less than that of a CD-R. (Please ignore the fact that I’m showing “-“ instead of “+”. I’m using “-“ in a generic sense. I could find no evidence that there was a lifespan difference in the competing “plus” and “minus” technologies.) A CD-RW can be written about 1000 times. Each media write breaks down the dye layer, so it seems to make sense that a CD-RW written 999 times would probably have a very short shelf life.

I saw one claim repeated several times, so therefore it must be true: The CD technology (not necessarily found the junk you might by for $0.10) will allow a CD-R to last for 50-200 years. And a CD-RW will last for 20-100 years. Wow.

This got me thinking about what my grandchildren would do if they were given a CD in 50 years. Would they even recognize it? If they did, would they have a CD player that could read it? I would certainly recognize an 8 ½” floppy disk, but I have long since lost any ability to read them. Heck, I’ve got CDs that currently won’t play in a CD player just a few years old. At the rate of technology change, I have trouble envisioning reliably reading CDs in just 10 years.

Anyway, I hope you suffered through this random rambling of half-truths and came to your own conclusion. My conclusion is that I’ll probably start buying more expensive CDs, and I’ll start storing them in more environmentally friendly conditions. And I’ll certainly keep two copies of everything. And I expect in a few years I’ll copy everything I still care about to HD-DVD or Blue Ray DVD, depending on who wins the war.

Good luck, and happy burning!

TT

This entry was posted on Wednesday, March 29th, 2006 and is filed under Storage Applications, Advisor - Tom. You can follow any responses to this entry through the RSS 2.0 feed. You can skip to the end and leave a response. Pinging is currently not allowed.