Monday, March 03, 2008

Compact Disc Life Span

Keyword Search: “How long will CDs last?”

This is a question that I researched extensively prior to switching to digital. The answers I found were less than satisfying. The problem stems from the fact that CDs are a relatively new medium, so information about long-term aging is not available. However, tests which simulate long-term aging have been conducted by several organizations in an attempt to determine the viable shelf life of CDs.

These tests provided some valuable data about the strengths of CD components. CDs have three main layers. The first layer consists of clear polycarbonate plastic. The second layer is a sheet of very thin reflective aluminum or gold. The third layer is acrylic and is the side that can have a label attached. CD-Rs have an extra dye layer between the plastic layer and the reflective layer. CD-RWs have a phase change layer and two dielectric layers in place of the dye layer. Plastic and acrylic have incredibly long shelf lives. Since the other layers are sandwiched between the two, they are well protected.

The tests also provided some valuable data about the weaknesses of CD components. Primarily, the method used to combine the layers. Separation seemed to be the main problem during the tests. There did not appear to be a significant difference between archival quality CDs and standard CDs during the testing. Also, since CD-Rs and CD-RWs have light sensitive layers, exposure to sunlight can cause degradation of the data on the CD.

Because these tests were designed to simulate the aging-process, facts about the actual life span of a CD have not been determined. Estimates range from a few years to several decades. I contacted several organizations that utilized CDs for long-term data storage and none of them had experienced any issues regarding the age of a CD. I have used CDs to store crime scene photographs for about six years and have not experienced any CD failures due to age. The most common errors are produced by physical damage to the CD and exposure to sunlight – just like 35mm film. I am not concerned about the shelf-life of CDs. My priority is on the care given to their storage – just like 35mm film.

What does worry me, however, is the speed at which technology changes the world. In the last few decades, computers have gone from 5 ¼” floppy diskettes to 3 ½” floppy diskettes to tape drives to Zip drives to CD drives to DVD drives…etc. I just need to make sure that I transfer all of the CDs to the latest format before compact disk drives head down the road toward extinction. I find it hard to believe that this will occur in the next few decades, but then again, who would have thought ten years ago that you could log on to your computer with a fingerprint swipe?

If you or your department is thinking of switching to digital and are hesitating due to the question of CD life, I would advise you to make the switch. Many photo labs are dropping their dedicated 35mm printers for equipment with digital capabilities. In my opinion, 35mm film will become obsolete long before digital media.

For more information about CDs, take a look at There is a very informative article by Marshall Brain explaining how CDs work and another article by Tom Harris regarding CD burners.