Mudcat Café message #702895 The Mudcat Café TM
Thread #47161   Message #702895
Posted By: JohnInKansas
02-May-02 - 11:07 AM
Thread Name: TECH: How long do CDRs last?
Subject: RE: TECH: How long do CDRs last?
treewind -

Looks like a good site - I'll get further into it later. As a user-group FAQ though, it still just skims the surface with "somebody's opinions." Hopefully there may be some leads to some physical data there.

The "plastic" used as the base for the disks in either type, CD or CD-R, should be fairly stable, although it would be necessary to know fairly precise formulations for the materials to guess about the basic dimensional stability of the material. IF the data is written as dimensional changes to a surface, you've got a "mechanical device" that should last a long time under good storage conditions.

The reflector that is bonded onto the back of the disk is also critical. The metal itself, any bonding agent used, and any crystallographic stresses produced either by bonding or by the recording process may affect how long the disk is "stable."

If the data is written by changing the crystallization of the plastic, then self-annealing will occur, and the data will change. Rates can be predicted for some material combinations; but again, it is necessary to know the precise material combinations and what changes are made in recording the data.

If the data is written by "burning" or "smudging" the reflector, then you need to know whether this affects the bond between disk and reflector, as well as the crytallographic properties of both parts, in order to make any reliably guesses.

Unfortunately, most of what I'd like to know about these things is probably considered "proprietary" by the disk and drive manufacturers, and they're not making it available.

Suffice to say that "I've had it with ZIP drives" - too many disk failures. Floppies simply don't provide enough storage space to be useful. I've tried tape: backup is easy, but I've never gotten a fully successful restore of anything of significant size.

At the present time, the CD-R is the method of choice for data storage off the hard drive. I would not however recommend that anyone treat the longevity of CD-Rs as a "given" in any "archival" situation. (That's an IMNSHO, of course). Data maintenance is still needed.