It's never a good idea to toss out a computer or hard drive before ensuring that all of the data on the drive has been completely erased. Standard file deletion only removes references to the deleted file and adds it to the hard drive's free space. And if the deleted files aren't overwritten, they can be retrieved with relative ease. But with the help of some free software, you can completely erase your hard drive before discarding it.
Download and install a copy of Active@ Kill Disk to erase your hard drive (see Resources). Active@ Kill Disk can be used to erase both used and unused space on your computer's hard drive, which ensures that deleted files can't be recovered. Every bit of data is overwritten with zeros. Active@ Kill Disk comes in three types: a Windows, DOS and Bootable version.
Use Eraser to wipe the data from your old computer's hard drive (see Resources). If you're intimidated by DOS-based utilities or are not comfortable accessing your computer's BIOS to set up bootable programs, then the Windows-based Eraser utility may be just what you need. Eraser let's you completely erase files, both current and deleted--so previously deleted files can be retrieved and permanently removed.
Erase any hard drive in your computer system using DBAN (see Resources). After copying the program to a removable medium, such as USB jump drive or CD, DBAN will be launched the next time you start up your computer. After booting up, DBAN will search for hard drives in your computer, and will completely erase the data on any hard drives found.