DVD DL MEDIA
DVD DL media represents the pinnacle achievement in a quest that started way back in the '60s with the first patent granted for an optical storage system. New formats like Blu-ray Disc have superseded the technological advancement that would have belonged to dual-layered technologies like DVD-9, but for a time DVD DL media promised to open up a whole new frontier.
As it is, the doubling of capacity offered by DVD DL media has been much, much more than surpassed by successor formats like Blu-ray Disc. And so this is a good time to review some of the fundamental characteristics of the optical disc, by way of recalling all the promise and excitement that once was. For the advent of optical disc storage media was a watershed event in human history. So much more data could now be stored in a fraction of the space required by previous superceded formats, and digital optical storage schemes form the standard for institutional archivists everywhere.
Librarians and archivists in general place great stock in the ability to preserve content faithfully while enabling its access daily. These two goals appear to have finally been met with the introduction of the DVD format, which allows for virtually eternal playback with no degradation whatsoever involved, unlike the situation offered by a medium like videotape. It has been noted, however, that analog-to-digital conversions are not always totally faithful due to less-than-optimal sampling rates and compression algorithms. Digital-to-digital copies, however, are exactly alike one another.
The power to make exact replicas where all-digital material is concerned means that it is possible, not to mention thoroughly recommended, for the original to be stored away while the copy is used for any and all playback. Under such a proposal, originals would only need to be handled when being inspected, used for the manufacture of additional copies, or migration to even newer formats. The practice of archiving originals also helps to ensure disaster, theft, and mishandling. Anything archived ought to be of limited access, stowed in a controlled environment apart from frequently accessed copies. This also enhances security concerns, helping to prevent data loss by theft, disaster, or mishandling.
Should budgetary restrictions rule out the use of separate locations, multiple copies need to be very carefully distinguished between those marked as “archival” and those as “accessible.” Should the material itself be one born analog, dual archiving ought to be practiced, where the analog original and the digitally mastered copy are available for future access.
But what is the life expectancy of a disc? It is actually hard to say. For one thing, it depends on what is meant by the term “life expectancy.” The phrase is generally used to suggest some length of time during which the disc remains usable. But such thinking implies an acceptable amount of degradation – which leads to the question of how much degradation is acceptable.
As there are different kinds of degradation possible, the issue can become more complicated than it would at first appear. Manufacturers typically use various accelerated aging processes to estimate longevity, and the results have been interpreted to mean this: 100 to 200 years or more for CD-R, DVD-R, and DVD+R discs, and only 25 years or more for CD-RW, DVD-RW, DVD+RW, and DVD-RAM discs. Curiously enough, there is little information regarding DVD-ROM discs, which comprise the majority of commercially available video and audio today, with opinions ranging from twenty years to one hundred.