The National Institute of Standards and Technology (NIST) Special Publication 800-88 recommends a number of methods for sanitizing electronic data on hard drives and other electronic media.
This is the standard TBS Industries adheres to in our hard drive wiping operations. This process may include overwriting not only the logical storage location of a file(s) (e.g., file allocation table) to be erased or deleted, but also the entire media including all addressable locations. The security goal of the overwriting process is to replace sensitive data with nonsensitive random data. Media should be overwritten a minimum of three times using a method based on the information sensitivity contained on the media.