Leaving fewer pieces behind...

Most people are at-least vaguely aware that when files are deleted from a computer, they still remain around for an indeterminate amount of time. Essentially what is happening is that when the file is deleted, a bit is marked on the disk telling the file system that the next piece of data that needs to occupy this "spot" on the disk, can do so - thusly overwriting the remnants of the deleted file.

When you are ready to donate or dispose of your computer, it is prudent to remove its information by way of  securely wiping your hard disk. I have seen some reports lately of discarded data coming back to haunt people. This is surely one way to fall victim to identity theft or be in violation of privacy laws when customer data is at stake.

Securely wiping your machine is a relatively simple operation. My favorite utility to accomplish this is Darik's Boot and Nuke. This utility allows you to make a bootable CD or Floppy disk that can be used to boot your computer and subsequently wipe all information from the disk using security standards that range from very secure to KGB-proof. You should expect this wiping process to take some time, especially if this is the old IBM XT 5160 sitting in your closet.

Do yourself a favor and make sure to wipe (or have wiped) your hard drive clean before donating or discarding your old PCs or hard drives.