How do I erase the data in a Windows 7 running laptop completely and make it irretrievable?

[Jacob D. McDaniels]

I am going to exchange my old laptop. And I would like to know steps of precautions to be taken before handing it over.

 

[Jacob D. McDaniels]

Method 1

1. Backup your data.
2. Download Knoppix Linux.
3. Burn it to a CD/DVD/USB.
4. Boot from it.
5. Open a terminal.
6. Type
   sudo dd if=/dev/zero of=/dev/sda
   and hit Enter.
7. Wait.
8. You're done!

Method 2 (if the first doesn't work):
Warning: This utility charges money for guaranteed erasing or for SSD erasing.

1. Backup your data.
2. Download dban (Darik's Boot And Nuke), a popular computer wiping utility.
3. Burn it to a USB drive and boot from it.
4. Type
   autonuke
   in the prompt and hit Enter.
5. Wait.