I hate that I have to ask this (re: disk errors).

[Skoorb]

I've seen scans of burned discs, be they DVD or CD, or whatever. In many/all cases it seems that burning inherently is accompanied by some errors. So, I take it to mean that if you have data that you've copied to a disc, that data is not being copied 100% perfectly. So, in some cases you have an 0110 in the source, and maybe an 0010 in the target disc.

If this is indeed the case, why don't these errors cause more problems? I know that with application code, for instance, a single missed character can blow an entire program up, so why doesn't this occur with information copied to a disk? If we burn an essay, how come when we pull it back it's not occasionally got a u turned into a t or something? Error correcting? How does it correct?

[skebenin]

I'm not sure what you mean by scans. If we're talking raw pits and lands, then yes there are write errors at that level. But then, there are errors at this level with pressed disks too.

What saves the day is error correction. Every sector on the disk includes some error correction data. The drive firmware uses the error correction data to recover from any physical errors on the raw media.

Error correction on CD-ROM data disks is pretty robust, and error correction on DVDs (which are all data disks) is a lot better.

[Skoorb]

I'm not sure what you mean by scans. If we're talking raw pits and lands, then yes there are write errors at that level. But then, there are errors at this level with pressed disks too.

What saves the day is error correction. Every sector on the disk includes some error correction data. The drive firmware uses the error correction data to recover from any physical errors on the raw media.

Error correction on CD-ROM data disks is pretty robust, and error correction on DVDs (which are all data disks) is a lot better.

Scans I mean just people's automated reading of a disk checking for errors.

On the minute level though, how can the error checking know what it has to do? I mean, if what used to be a 1 is now a 0 or vice versa, how can the disk know that? And if it can't, how is it that programs, which often rely on an exact charcter, still work without issue? Surely an Mp3 may not matter or a long video file (since a bad bit could just be a glitch on a single frame that you'd never see), but something more essential would seem to me to cause a run time error, or something similar.

[skebenin]

Scans of CD-DA (compact disk - digital audio) will often show erros. That's because CD-DA has little error correction (or is it no error correction). However, CD-ROM and DVD-ROM (with the error correction) really should show very few errors at the logical read (data) level.

I suspect explaining error correction would be difficult, even if I did understand it. Rather than even try, I think it best to refer you to information on the web. A quick google turned this up for example:
http://en.wikipedia.org/wiki/Reed-Solomon_error_correction