What is the Difference Between "Delete" and "Erase"?
When a file becomes sufficiently out of date to offer no archival value, you can consign the document to your Recycle Bin or Trash on Microsoft Windows and OS X, respectively. Trashing a file doesn't remove it from your hard drive. If you've ever accidentally deleted the wrong document and fished it out just before emptying your computer trash, you know that you can reverse the first step in the deletion process with ease -- as long as you haven't set up your system to get rid of files the moment you trash them. The act of emptying your Recycle Bin or Trash tells your OS that it can reclaim the space occupied by deleted files for use with new data. Until new information takes over that disk space, the information you deleted remains recoverable. If you write a smaller file onto the space occupied by a larger one, part of the deleted document remains. Because hard drives store data in chunks of fixed sizes, most documents include slack space, a small amount of unused storage after the active data and before the file's allocated size. Information from deleted files can remain accessible in slack space.
Erasing a hard drive before you reinstall your operating system doesn't necessarily get rid of the information on the disk, but it takes a step closer to that eventuality than simple deletion does. When you issue an erasure command in a disk formatting program, you get rid of the hidden files that tell your OS how you partitioned your drive. This step can prepare the drive for reuse, but it doesn't actually remove the data from the storage mechanism. To give this procedure a more secure result, you can opt for erasure steps that replace drive information with random data or a repeated pattern of ones or zeroes.