The beautiful part of it all is the reason why that hacking or the use of software is able to work. See, files and data never really leave the hard drive, even if you erase the entire thing. All of the data, in one form or another, remains there. It imbeds itself into little hiding places on your hard drive and waits to be coaxed out. Even if a virus ruins your entire computer, forcing you to erase everything and start afresh, reinstalling your OS and everything, you can still retrieve all of the previous data that was there before you erased everything.
That is basically how to retrieve deleted files - it's all a matter of knowing that they still exist somewhere on your hard drive, and knowing how to pull it all out of their hiding places. This is what data retrieval software does for you. It's a lot like having your own computer hacking task force at your beck and call, ready to do your bidding at the click of a mouse. Data retrieval software is definitely how to retrieve deleted files.