When recovering a deleted file, the program checks to see if the file has been overwritten with other data. In technical terms, it reads the File Allocation Table (FAT) or Master File Table (MFT) to determine if the space used by the deleted file is being occupied by other active files.

As only one file can occupy a storage space at any one time, if a deleted file has been overwritten or partially overwritten, the overwritten part of the deleted file has been destroyed.

In most searches you will see a column called "Recovery" in the results screen. This column is an indication as to whether the file has been overwritten. The rating system is as follows:

• Overwritten: The original file has been completely overwritten and cannot be recovered.
• Poor: the search indicates that between 1% and 50% of the file can be recovered.
• Medium: the search indicates that between 51% and 90% of the file can be recovered.
• Good: the search indicates that between 91% and 99% of the file can be recovered.
• Very Good: there is no indication that the file has been overwritten. The complete file can be recovered (check to see if a preview is available).

While this rating system is a good indication of the chance of recovery, a preview of your file, if available, is the definitive way to determine if your file can be recovered.

In many circumstances, it is possible to recover a partially corrupt file and open it with the creating application. There are also programs on the Internet which will repair certain file types which have become corrupt.