As you probably know, formatting a hard drive doesn’t completely erase the data on it. You must overwrite the data to securely destroy it, preferably multiple times. Windows 8 let’s you do this with the format command and the /p parameter.
We’ve covered how to do a secure erase before
Format H: /P:7
The number after /P: is the number of secure erases Windows performs (so in this case it’s a total of 7).
Source : LifeHacker