How do you permanently delete files off your hard drive?

Every once in a while we have a customer asking about how to permanently delete files from their computer, so that no one can ever find them again.  The answer is easy.  Destroy your hard drive by melting in in a fire or by dissolving it in acid.  At Excel Computers, we offer our means of getting the job accomplished by placing our customer's old hard drives in a plastic bag and slamming it on the ground, effectively smashing them.

A more textbook explaination of how a hard drive works is this:  Files are written onto your drive as a series of ones and zeroes.  A directory of that file tells the computer where it is.  When you delete a file, you change that directory.  Your computer will no longer find it, but the data may still exist until something else writes over it, changing those ones and zeroes into a different series of ones and zeroes. 

For those looking to give away a functional computer and/or not wanting to smash their old hard drives, there are programs which promise to permanently delete these files so that they are no longer readable.  Some of these programs can work better than others at making overwritten data irretrievable.  While we're not the FBI or have any high tech forensic capabilities here, we've found that these hard drive erasing programs will make it virtually impossible for anyone other than supreme hackers or law enforcement to even have a chance at recovering erased data.  

A good open source free hard drive erasing program that we've had good experience with is Eraser (http://www.heidi.ie/node/6).  Eraser is compatible with all versions of Windows from 95 on up and performs all of its functions within Windows.  Erasing your hard drive is your only choice if you intend on leaving it funtional.  But if you have a computer on which you’ve stored sensitive data, the only way to be 100 percent sure it’s gone is to destroy the hard drive.