CD Bit Rot

For my Management of Business Information Systems class, we had to write a summary paper on an article in the news that pertained to information technology. I found an article in the Fort Wayne Journal Gazette describing Bit Rot. Below is my summary.

Compact Disc "Bit Rot"

Svensson, Peter; "CDs, DVDs: Handle with care to prevent disc rot" Fort Wayne Journal Gazette (May 10, 2004)

Long thought to be the indestructible media of the future, compact discs and DVDs are beginning to show signs of vulnerability. The media, which was first introduced 80's, is manufactured simply enough. The disc is composed of a plastic wafer with a thin metal film applied to the top. This metal film is then coated to protect it, and to allow the application of a label. As the disc spins, a laser beam is reflected off of the bottom of the disc. Small pits in the disc allow the beam to be either reflected or scattered, translating into the binary 1's and 0's that computers understand. The media was designed such that scratches to the bottom surface would not prevent the media from being read.
Although the bottom of the disc is clearly protected, the top of the disc is strangely vulnerable to defects. The metal film which contains the information for the disc is only protected by a thing coating from the top of the disc. This thin coating can be destroyed by the very minor scratches, such as from a ball point pen or stacking with other discs. Once damaged, the metal film is exposed to the air, and this can allow the media to oxidize, much like the body panels on a car rust. Once the damage is done, it is irreversible, and can completely consume the disc.

Bit rot, as this phenomenon is termed, can be catastrophic to IT departments attempting to archive their data. Federal regulations and corporate policies often require that data be stored and retrievable for seven years and longer. Compact discs were seen as the cheap alternative to tape backup, and were thought to be much more reliable. Now archivists must scramble to ensure that this data is not destroyed by bit rot, and find a more reliable alternative for storage.


Jade Mason