Message-Id: <199610172224.RAA24305@library.wustl.edu> Date: Fri, 18 Oct 1996 00:13:08 +0200 From: "Trock, Jacob" <mailto:jacob.trock@POST3.TELE.DK> Subject: Re: image storage To: Multiple recipients of list IMAGELIB
Here is my contribution to the discussion on image storing:
About longevity of CD's: No one can tell for sure how long they will last. If you put all the defferent Accelerated agening tests together you probably wil see that mass-produced CD's (CD-A & CD-ROM) will last from everything between 5 to 200 years. The same could be said about CD-R's. And probably everyone have right.
There are good disks, and there are bad disks. It all depends on how they were manufactured and later handled and stored.
What I have come to is, that it is very important that the disc is "born" under the best conditions. This means that CD-A and CD-ROM are produced with a not to thin aluminium-layer, that the Poly-carbonate is resistand towards humidity (most of them are) and most important that the top coat (resin) is good.E.g. "Century"-disks are CD-ROM's with an extra thick layer of resin.
The same for CD-R's. It is important that the disk is "toasted" with the right laserpower for the specific media. Cyanine-dye based CDšs require a different level of laserpower than the competitive pthalocyanine-dye based disc. Ask your local dealer before you go out buying 100 CD-R's. There are both prošs and con's for both media types, but if they are made correct they will probably last longer than the technology. (There is a lot about this topic on the net)
About formats: The best way to store data is using the most simple format appropriate for the job. Use standards! (even though standards mostly never are one thing, they change like we change underwear;-). Use a format that your colleagues use, and as many other too. The more people in the same boat, the better is the possibility that software and hardware vendors will listen to your problem.
What brings us to the word you always have to remember, talking digital storage:
OBSOLESCENCE!
Here will the CD-media have the great advantage that this media is the most used format in the world, maybe after the 3,5" diskette. This gives us the best guarantee that we at least will be able to migrate data in good time to what ever media that comes next.
What again brings us to the next important word:
MIGRATION!
If you want to store digital data for more than 5 to 10 years, migration is inevitable. So storing digital data for the future gives certain obligations for the Institution that makes this decission. This is the most essential part of preserving digital data, and maybe the most vulnerable!