What You Think Happens
So you’ve got a confidential, secretive or naughty (dare I say it) file you wish to delete from your computer. You go on and right click, then press delete, after which you Empty the Recycle Bin (or “Trash” for Mac Users). The file is now gone forever and nobody would ever know you had it.
But then you would be wrong…
What ACTUALLY Happens
When you empty the Recycle Bin or Trash, your computer doesn’t actually remove the physical file on the hard drive. Instead, it takes a lazy route and deletes the reference in the file table to the file at the start of the hard disk, making it “invisible” to the Operating System. The actual file is untouched on your Hard Drive, until another file writes over the “deleted file”.
It’s a bit like removing someones name from the phone directory, you won’t be able to find it, but the person concerned still exists; and if you knock on every door, you’ll eventually find them.
Why Does it Do that?
It’s mainly to do with user experience. Ever wonder why it takes so long to copy large files onto your computer, but why deleting large files is almost instantaneous? To actually delete the entire file and remove it from the hard drive would take enormous amounts of time and energy, so emptying your recycle bin would take much, much longer than it does normally. By only removing the reference to the file, your computer can “complete” the operation much faster, idle sooner, put less wear on the hard drive and provide a more responsive user experience.
Just take this example…
Deleting 14GB of large files “normally”: 2 Seconds
Deleting 14GB of large files “securely” (properly): 14 Minutes
And it’s not just the files you delete, the operating system deletes temporary or cache files from the hard drive all the time, and the performance penalty of the OS removing these files properly would slow down the user experience drastically.
How to Delete Stuff PERMANENTLY
So you’ve got stuff you don’t wan’t anyone to see, and you want to hide the evidence? Luckily there is a way to delete files from a hard drive more safely.
On MacOS, selecting “Secure Empty Trash” from the finder menu would write zero’s over the files you wish to delete (over-writing replaces the file data with blank space). Note that while this would hide any trace of the file which would be visible to the computer (even to file “undelete” or recover software), advanced techniques (beyond the scope of this post) are available which could recover data even if it has been overwritten.
On Windows, Third Party software such as Eraser can be used to securely delete files. As before, even when securely deleting files, it may still be possible to retrieve data using advanced techniques.
And just a word of warning, re-formatting your hard drive may not remove everything. You may be familiar with “Quick Re-Format”, which essentially removes the file system table, but keeps all the data intact. Some other methods of re-formatting do the same thing To erase a hard drive, USB stick or any other storage medium securely, simply destroy it (properly, i.e. burn, crush, tear etc etc), making sure you destroy the actual media where the data is stored (i.e. the disk platter or the flash “chip”).