How does file recovery software work?

Question

I wanted to make some simple file recovery software, where I want to try to recover files which happen to have been deleted by pressing Shift + Delete. I'm working in Windows, can anyone show me any links or documents which can help me to do so programatically? I know C, C++, .NET. Any pointers?

Answer 1

http://www.google.hu/search?q=file+recovery+theory&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a :)

Mainly file recoveries are looking for file headers and/or filenames in the disk as I know, then try to get the whole file by the header information.

This could be a good start: http://geeksaresexy.blogspot.com/2006/02/theory-behind-deleted-files-recovery.html

Answer 2

The principle of all recovery tools is that deleting a file only removes a pointer in a folder and (quick) formatting of a partition only rewrites the first sectors of the partition which contains the headers of the filesystem. An in depth analysis of the partition data (at sector level) can rebuild a big part of the filesystem data, cluster allocation tables, folders, and file cluster chains.

All course if you use a surface test tool while formatting the partition that will rewrite all sectors to make sure that they are correct, nothing will be recoverable - unless you use specialized hardware to look at remanent magnetism on the edges of the actual tracks

Answer 3

In windows when a file is deleted(permanent delete) it's not actually deleted from disk but the file name added with char( _ I guess) in front of it and windows ignores these when showing in explorer... and recovery tools will search these kind of file names in the disk. And your file recover integrity based on some data over written on location of deleted file. Don't know this pattern still used by windows.. but long time back I have read this some where