Hard Drive Software What Software To Buy To Completely Erase My Hard Drive?

What Software to Buy To Completely Erase My Hard Drive? - hard drive software

Selling my laptop, but we know that is not the contents of the hard drive and reinstalling the operating system sufficient to completely clean the hard drive. What software can I buy, will they work? I want to buy in a store as a download, free, and everything that is not addressed to me, like he knows what is going to download it. The recommendations of decent software would be welcomed!