Well all CDs (and DVDs for that matter) have errors on them, even the best ones. If you look at some of Ian's reviews here, you'll see that in the tests.
Basically (and I know this is a gross oversimplification guys, but bear with me
) on a CDR there are 3 levels of error: C1 error, which is completely normal and is handled by the error correction process, C2 error, which is a more serious error and can only sometimes be masked by the system, and an unreadable sector (terminal!)
A disc can have hundreds of thousands of C1 errors and still be totally readable. But when there's a scratch, or a shadow, or just an area of the disc that's badly manufactured, this area suffers an increase of C1 errors. The disc is still 100% readable, but there is always the chance that this area could get worse over time -- if the disc is going to deteriorate (and all discs do over time), this bad area will suffer first. So whereas a clean disc may last 15 or 20 years, that one small area may only last 3 or 4.
Think of it like when you're shaving. You could have a small spot on your face. This spot causes no pain, and normally shaving doesn't cut the skin unless you keep shaving and shaving until you eventually tear the skin, but if you shave over the spot, you'll be in agony on that one small area. Same sort of thing; the deterioration applies uniformly over the disc, but each time the disc deteriorates by a certain amount, that bad area is being brought closer to the point where you can't read it any more, and will get there sooner than if it wasn't there.
For non-critical data, it doesn't matter one jot. But if you need to keep the disc over the longer term, copy it onto another disc.
by johnnyz on Tue Apr 29, 2003 2:06 am 
