mardi 30 janvier 2007, par anass
Ever since their appearance on the market in the early 1990s, recordable compacts discs (CD-Rs), later recordable DVDs and now recordable blue laser discs formats have been used as storage media not only for private purposes, but also for the storage of digitised or born-digital documents in archives and libraries. The attraction to employ these recording media lies in their easy availability and, most importantly, in the low prices of media and recording/replay equipment.
The use of CD and DVD recordable discs in archives and libraries has soon raised concerns as to their reliability as storage media. Most of these concerns have focussed on the issue of life expectancy of the media themselves, concluding that different types of dyes, recording substrates, and reflective layers behave differently. The problem, however, is more complex. The quality of the recorded digital signal is an important factor of life expectancy. This quality, however, relies on the interaction of the individual burner, the medium, and the individual player. As burners and players are not standardised, the data quality and life expectancy is to some extent unpredictable. Unless the data quality is systematically tested using reliable professional testers the quality of the content is unknown and consequently at risk. Testing is possible ; however, reliable testing is time consuming, dependant on manual systems and in need of expensive test equipment.
While recordable optical discs are viable tools in the access to and dissemination of digital information of all kinds, it is strongly recommended that professional data storage methods, as developed by the IT industry, should be used. All digital carriers are to some extent unreliable, however, data tape and hard disc systems are made reliable because technological testing, copying and management systems are implemented to support the data carrier and the quality of its content, maintain and manage the integrity of the data. These systems are feasible for storing critical data even under climatically and financially sub-optimal conditions. No viable automatic testing and management system exists to make optical disc reliable, and consequently any archival use of optical systems must depend on a manual approach using people and testing equipment as described in this publication.
Source : Unesco.2006. Auteur :Kevin Bradley.