Åjaa..er det derfor SACD låter bedre enn CD ? ;D
Nå må du slutte å tøve.
http://www.storagereview.com/guide2000/ref/hdd/geom/error.html
"Many people don't realize that it is normal for a hard disk to encounter errors during reading, as part of its regular operation. As hard disks are pushed to the limits of technology, with tracks and sectors spaced closer together, weaker signals used to prevent interference, and faster spin rates produced by the spindle motor, the chances of an error occurring while reading the disk go up dramatically. In fact, the state of technology has advanced to the point where it is not practical to even try to avoid them.
Of course having actual errors appear to you while using the hard disk is unacceptable, since you count on your disk reproducing the data you store on it reliably, for a period of years. Hard disk manufacturers know how important this is, and so incorporate special techniques that allow them to detect and correct hard disk errors. This allows them to make faster, higher-capacity drives that appear to the user to be error-free. The more the technology for storing data is pushed, the more sophisticated the error correction protocols must be to maintain the same level of reliability.
Making a drive that actually produced read errors infrequently enough that error detection and correction wasn't necessary, would mean greatly reducing performance and capacity. This is sort of like touch-typing: there's a school of thought that says "if you aren't making any mistakes at all, you're going too slow". If correcting mistakes is easy, as it is with a word-processor, it's better to type 100 words per minute and correct an error or two, than to type 75 words per minute error-free. As long as the errors are detectable and correctable, and they don't occur too often, it's better to plan for them, and then tolerate and deal with them, than to be too conservative in order to eliminate them.
...
When a sector is written to the hard disk, the appropriate ECC codes are generated and stored in the bits reserved for them. When the sector is read back, the user data read, combined with the ECC bits, can tell the controller if any errors occurred during the read. Errors that can be corrected using the redundant information are corrected before passing the data to the rest of the system. The system can also tell when there is too much damage to the data to correct, and will issue an error notification in that event. The sophisticated firmware present in all modern drives uses ECC as part of its overall error management protocols. This is all done "on the fly" with no intervention from the user required, and no slowdown in performance even when errors are encountered and must be corrected.
The capability of a Reed Solomon ECC implementation is based on the number of additional ECC bits it includes. The more bits that are included for a given amount of data, the more errors that can be tolerated. There are multiple tradeoffs involved in deciding how many bits of ECC information to use. Including more bits per sector of data allows for more robust error detection and correction, but means fewer sectors can be put on each track, since more of the linear distance of the track is used up with non-data bits
"
-k
