Andrew Whitehead is a contributor at Free-backup.info — the home of the popular tool for windows online backup — Back2zip. This article can be found at http://free-backup.info/the-principles-of-file-recovery.html
Why File Recovery is Possible
File recovery is nearly always possible, if you spot the mistake and do something about it fast enough. Luckily, if you do mistakenly delete a file, the file has not been physically removed, the operating system just doesn’t know where it is anymore. This is easier to understand once you realize that there is more to storing a file on your hard drive than just finding space for the information and writing it there.
The operating system must also keep track of where it put the file, without this it would be unable to find it again. When a file gets deleted, this record is altered and the disk area containing the information is marked as free space. The information itself remains intact until some other information is written over it.
The effect is similar to rubbing out the name of a video tape – you know you can use that tape now, but the original film is still on there until you do it, and should you change your mind you can do your own ‘file recovery‘ by writing the name on the box again. Commercial file recovery programs do exactly the same trick with computer files.
File Recovery Programs
There is no shortage of file recovery software to help you out if you delete the wrong file. There are numerous commercial file recovery programs, DOS has its own ‘Undelete’ command, and Windows has the familiar Recycle Bin. Except for Recycle Bin, they all work on the same principle of searching the hard drive for files that have recently been marked for overwriting. More advanced ones will also tell you how much of the file is recoverable by checking how much has been written over.
The seemingly simple Recycle Bin has one advantage over any third party file recovery program: it doesn’t allow any overwriting of deleted files stored in there. This means that files from here are recovered in their entirety, and will function exactly as before once they are restored.
Obstacles to File Recovery
The biggest obstacle by far is time. The longer you wait, the higher the chance of a deleted file being written over, unless it is safely in the Recycle Bin. Once this has happened file recovery is still possible but it will take a lot more than a bit of commercial software to do it.
Operating systems are continuously creating files, every web page you visit does the same, and so does every application you open. With this in mind, the time to start your file recovery process is the instant that you realize you needed that file.
If you are extremely security conscious enough to be running encryption software this will also reduce your chances of file recovery, as the majority of file recovery programs need to read the file to know it is there. If the encryption utility doesn’t offer its own built-in undelete function then file recovery is going to be very difficult and very expensive.
