Data Recovery is a method of salvaging data lost from a storage medium, may it be due to corruption of the data, physical damage to the storage medium, etc when it cannot be accessed normally due to certain issues.
One of the few scenarios where this happens is an OS(operating system) failure. The data recovery method is simply to copy all the wanted and important files to another medium, as they cannot be accessed by the operating system which fails to boot. This can be easily done by using a OS Live CD, which provide a means to mount the system drive and all the disks and removable media, and to move the files from the system disks which contain the operating system to the disks and medias with a file manager/optical disc authoring software.
Another scenario involves a disk-level failure, such as a compromised file system/disk partition/hard disk failure. Reading data from these cases would seem almost futile. Depending on the situation, solutions involve repairing the file system, partition table, the master boot record or even using advanced hard-disk recovery software which reads all the data contained in the system, no matter what condition it is in.
The third scenario involves files being deleted accidentally/purposely from the storage media. In fact, they are not even deleted permanently. For example, in Windows, when you delete a file, you can recover it in the recycle bin. And even if you delete it permanently, it is still in the hard disk. Windows marks these files as “deleted” files and makes them invisible so that the user does not see them. Disk space is also seen as increasing, but in reality, it stays the same. When you want to copy a file, then Windows will overwrite the deleted file by adding the copied file. This is the mechanism of Windows file deletion.
To view/restore these invisible files, you can unhide all the files with a special technique and find a folder called $RecyleBin(similar).
Here is a good professional software which you can use to “undelete” the deleted files in many scenarios, but you should always keep a backup to prepare for the worst:
Recover My Files
Recover My Files data recovery software will recover deleted files emptied from the Windows Recycle Bin, or lost due to the format or corruption of a hard drive, virus or Trojan infection, unexpected system shutdown or software failure. Also, it has many other useful products, mainly for data-recovery purposes. Visit their website to check them out.