formatting might not be enough every drive manufacturer has there own little program to write zero's and 1's
Answer Formating a hard drive prepares it for use and deletes previous file names so Windows can't see them. They still exist and can be recovered with several Undelete programs. However, if you wish to remove all data from the drive, just formatting is not enough. \"Zeroing\" a drive rewrites over the entire drive, replacing previous data with simple 0's. There are several 'Zero' filling programs available on the web and some drive manufacturers include a zero utility on their support sites.
Answer The previous answer is pretty good, however it is argued that you can recover a zeroed hard drive. It is possible to retrieve \"some\" data however \"fully recovering\" a zeroed hard drive hasn't been done as far as i know. simply doing a \"1 zero pass\" will invert all the \"1's\" to \"0's\" (remember there are only 1's and 0's) hence \"zeroing\" however there is software available that can detect newly magnetized \"0's\" it simply re-inverts the \"0's\" to \"1's\" if you do a \"7 zero pass\" it's pretty much impossible to retrieve any information off the hard drive. look into the \"DoD 5220.22-m\" standard or \"gutmann\". hope this is useful.