Three types of wipes are: Quick Wiper, DoD Standard Wipe, and the Gutman Wipe.

The Quick Wiper overwrites 1 time. This is very useful when you absolutely want to destroy all malware before a clean install. I use it on all drives before clean installs. It costs $30 for one computer.

The DoD Standard Wipe. This is what the Department of Defense has set as their Standard. This Wipe will overwrite 7 times. I have never heard of anything recovered from such a Wipe. This takes a very long time and often 3 wipes is more than sufficient.

The Gutman Wipe. This overwrites 35 times. People that believe they need this security should be medicated. The is Black Helicopter Paranoia.

A good freeware program is Darik's Boot and Nuke. Another product to check out is cyberCide Data Destruction.

Depending on your computer a Quick wipe can take 24 hours or more.