![]() The quality of the top protective layer is also important. However, the dye and metal reflective layers can be composed of various materials, and each has its own inherent stability. The base layer of a CD-R is always composed of polycarbonate. When a disc is read, a laser shines through the base of the disc, hits a laser-altered spot or non-spot area in the groove and gets reflected back by the metal reflective layer to a signal detector. On top of the dye recording layer is a metal reflective layer, followed by a protective layer and then a label. Within the dye layer in the grooves rest laser-altered dye spots representing the digital information. Both the groove and non-groove areas of the top of the plastic base are covered with a dye recording layer. Molded into the top of the plastic base is a spiral groove. Description of Figure 1Ī cross-section of a CD-R shows that most of the thickness of the disc is the plastic base. © Government of Canada, Canadian Conservation Institute. Materials used in disc manufacturing CD-RĬD-Rs are composed of several layers (Figure 1): Information on where the disc was actually produced may be available by consulting the manufacturer and/or examining coding on the disc. Even though some large manufacturers label discs produced elsewhere with their own brand name, most have no desire to be associated with an inferior product. In the absence of testing, discs with a recognized brand name can generally be assumed to be of good quality. This is not feasible for most archives, libraries and museums. Poor manufacturing is still a problem to some extent, either because of cost-cutting to meet competitive pricing or because of the growing lack of quality manufacturers producing these materials.ĭetermining if a disc is poorly manufactured is an impossible task without thorough testing, which likely would include accelerated aging. ![]() This was a significant problem when discs were introduced Endnote 2 and for at least two to three years afterwards. Poor-quality discs (discs that do not meet standard specifications for proper manufacturing and function) will probably fail sooner than good-quality ones, due to rapid chemical degradation or physical damage. This Note explores several of the factors that affect whether a disc will fail within a short period or will continue to perform well for many years. ![]() Research studies, anecdotal information and manufacturers’ literature suggest that the lifetime of recordable optical discs can range from a couple of years to more than 200 years. The longevity of recordable compact discs (CD-Rs), recordable digital versatile discs (DVD±Rs) Endnote 1 and recordable Blu-rays (BD-Rs) is uncertain, leading to a widespread lack of trust by libraries and archives. List of abbreviations BIS burst indication subcode BLER block error rate DL dual layer LDC long distance code PI8 parity inner error rate averaged over eight blocks Introduction
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