I just brought up an old PC from the cellar, vacuum-cleaned it and I'm now running Darik's Boot and Nuke to wipe the hard disk clean. That is going to take over two hours. DBAN is a bootable image, both for floppy disk and CD-ROM, which attempts to detect and optionally wipe all attached hard disks, something very useful to do before giving the computer away or even before trashing it. I'm passing the time by reading the FAQ:
Q: Why does my computer start into a black screen after using DBAN? A: You must reinstall an operating system because DBAN removes it.
Oh, yes. ;-)