Preservation of correspondence

aliensrcooluk at yahoo.co.uk wrote: The "ordinary" ones are pressed at a factory. A glass master (I _think_ it is glass) is produced and is used to press the CD. As long as it is assembled correctly (and especially, it seems, sealed around the edges) then that it likely to be the most stable form of CD. Unless something gets inside and starts to eat the aluminium, then it should be fine. (Obviously I'm excluding physical damage, etc.) For +/-R media the laser burns a pit in a special layer in the disc to create a pit. For the +/-RW forms the laser causes a reversible phase change to create an optical pit (heating it up again causes the change to reverse, hence blanking the pit). erased once they are written, although you can write a new table of contents (TOC), so that it looks like you have overwritten the old data, but in fact it is still there There are programs which will dig it out for you. I supposed theoretically you could blank a CD-R by burning every possible pit, but if you are security conscious, just break it (or shred it). When you "finalise" a DVD-R it can no longer be written to. I _think_ that all that has happened is that some bits have been set on a reserved area of the medium to tell the drive not to write to it any more. Unless you have a rogue drive (or maybe rogue software) then this is probably as safe as a floppy write-protect tab. The +/-RW forms can be fully erased and reused (1000x is the claim, yeah right!). Regardless of whether these are more or less stable than -R, they are clearly of limited use for long term archiving, since there is always a risk that they will get blanked and reused for "something more important". There's also DVD-RAM, but I don't think that's very important for our purposes. Then there is the whole +/- debate, but these days that has mostly died away. You ?20 (high-end :-)) DVD rewriter will write to CD-R,CD-RW,DVD-R,DVD+R,DVD-RW,DVD+RW,DVD-RAM and dual layer DVD-R (~8GB, but the disks are about 5x the cost of a DVD-R). Antonio