Data recovery is a process by which one can salvage electronic data from damaged and corrupted storage media which cannot be accessed through normal means.
Mostly, these storage devices are CDs / DVDs or hard disk drives, the physical or logical damage to which prevents the operating system from accessing the various locations on the media.
Types of media from which it has been done in the past are storage media like the HDD, the pen drive, storage tapes, CDs/DVDs, and some other optical media.
The commonest of all recovery issues figure in the hard drive and Raid, where the data becomes inaccessible.
Some other problems are related to files being deleted from the resident file system.
Using some techniques the so called deleted files can also be restored.
Then of course there are the hard disk failures for which data retrieval is essential.
Any sort of it's recovery, requires knowledge of why a media fails.
Recovering it from defunct, failed and damaged storage media is fast becoming a major business area and there are several companies which have formed a fair business model around it.
There are specific recovery services being offered by these companies which specialize in hard drive recovery.
Many firms also offer SQL data recovery which is a type of database recovery, Raid one and Mac one, especially for those Mac users.
They should have the experience to be able to deal with any sort of data recovery requirement, and specialize in it's recovery from all brands, storage device manufacturers, different interfaces of media, and different configurations.