Background: Optical discs can be convenient media for access and temporary storage. Unfortunately, such media are machine-dependent, so access is contingent on surviving and working hardware and software. Additionally, such media are subject to changing manufacturer standards, as well as deterioration, just like any other material.
Optical discs are made of many layers, and the materials used in these layers change over time, depending on how and when the discs were made and how they age. Depending on susceptibility, wear, and environment, various layers of optical discs may undergo oxidation, hydrolysis or mechanical stress, leading to damage (variously described as “rot” or “pin holes” or “mirroring”, etc.). These and other phenomenon may lead to errors in signal playback, which can be assessed by measuring a disc’s “block error rate” or BLER. The greater the BLER, the greater the loss of information.
The Information Access Division of the National Institute of Standards and Technology (NIST) and the Preservation Directorate at the Library of Congress agreed to perform a detailed investigation of the longevity of recordable Compact Disc (CD) and Digital Versatile Disc (DVD) media. The effort was aimed at estimating the life expectancy of information stored in CD-R, DVD-R and DVD+R, as well as DVD-RW and DVD+RW discs.
Contributing Study: NIST/Library of Congress Optical Disc Longevity Study: Final Report. Library of Congress and the National Institute of Standards and Technology, September 2007. [PDF: 404 KB / 32 p.]
Project Description: This project used accelerated aging techniques and statistical analysis to estimate the life expectancy (LE) of current recordable DVD and CD media. Only the effects of temperature and relative humidity on the media are considered. The standardized life expectancy estimated using this model is defined for discs maintained at 25ºC and 50% RH, but can be applied to give an estimate of the life expectancy at any moderate storage conditions. Discs exposed to more severe conditions of temperature and humidity would be expected to experience a shorter life. The testing did not attempt to model degradation due to exposure to light, corrosive gases, contaminants, or mishandling, nor does it account for variations in the playback subsystem.
Outcomes/Findings: The results of this effort are summarized below:
- An accelerated aging protocol, using various parameters of temperature and relative humidity, was successfully implemented for the variety of products in this study.
- It has been shown that different optical media products react to the various exposure conditions in very different ways. This makes analysis and predictions of these products very difficult and at best, this type of artificial aging testing only represents a broad estimate of the actual longevity of the media.
- Most CD products earned a high probability of prolonged lifetime relative to their DVD counterparts.