Comparison of recordable optical discs - Study of error rates in harsh conditions

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The reliability and longevity of any storage medium is a key issue for archivists and preservationists as well as for the creators of important information. This is particularly true in the case of digital media such as DVD and CD where a sufficient number of errors may render the disc unreadable. The National Institute of Standards and Technology (NIST) has published the results of their study CD/DVD longevity.

This paper describes an initial stability study of commercially available recordable DVD and CD media using accelerated aging tests under conditions of increased temperature and humidity. The effect of prolonged exposure to direct light is also investigated and shown to have an effect on the error rates of the media. Initial results show that high quality optical media have very stable characteristics and may be suitable for long-term storage applications. However, results also indicate that significant differences exist in the stability of recordable optical media from different manufacturers.

Some of the conclusions from the article:

While there are a number of factors that may contribute to the stability of the CD-R and DVD-R media, dye type is generally considered one of the more important ones. Based on the test results for CD-R media, this expectation appears to hold true, even with mixed results for the dye types. Samples containing phthalocyanine performed better than other dye types. In particular, phthalocyanine combined with a gold-silver alloy as a reflective layer was consistently more stable than all other types of CD-R media. Discs using azo dye as the data layer had less stability in light exposure and temperature/humidity stress testing. Media using cyanine dye performed well when exposed to light but had problems when under temperature/humidity stress conditions.

Although information is less accessible regarding the dye type used in DVD recordable media, it is believed that DVD-R media use a modified form of stabilized Cyanine dye for the recording layer. It is therefore difficult to make any determinations from these results based on dye types for DVD-R media. Furthermore, manufacturers make modifications to the dye to improve its stability or to make it less expensive. This process may result in similar dye types having considerably different qualities, which is shown to be the case in the DVD-R discs tested. And again, as in the case of the CD recordable media, the variation of stability among different brands of DVD recordable media is considerable.

Our results show that the effects of direct light exposure cannot be ignored. The spectral wavelength of metal halide is close to what may be expected within the higher spectrum of sunlight. Depending on the media type and intensity of the light, a disc may fail due to exposure to direct sunlight in as little as a few weeks. This will be especially true when coupled with the heating effect of exposure to sunlight or combined with any other heat source. For archival purposes, however, light is a less challenging issue since it is relatively simple to avoid direct light exposure or prolonged exposure to any damaging light source.

Some of you who will find the full article (PDF) an interesting read. We would also like to invite our readers to visit our DVD Media Reviews section for in-depth reviews of a wide variety of recordable DVD media. Feel welcome to share any of your experiences on media in our Media Forum