Data corruption on optical media is a common problem due to physical damage to the media like scratches, surprisingly data can still be recovered from non-readable scratched sectors on CD and DVD's using the following method.

A CD/DVD reader uses a laser beam to read the data on the disk. This laser beam crosses the protective plastic layer and reads the real recording metal layer. If the protective plastic layer is scratched, the laser will be unable to pass resulting in non-readable disc.