But now that this is here, there are two computers in this household that are going to be given their walking papers soon. How does one make sure nothing is left on it?
Formating is in general not the best ways to get rid of data on the hard drives, multiple formats or otherwise.
I use a program called DBan found at dban (dot) sourceforge (dot) net
which has wiping algorithms such as
American DoD 5220-22.M Standard Wipe
and the like.
Generally speaking this is over kill and time consuming but in theory it is safer then even using a sledge hammer...well, unless you literally pulverize the disc platters until they are just dust.
Otherwise, there are still ways professionals can extract data even from broken fragments of disc platers...albeit, someone who picks up a computer from trash is not going to go to the bother of doing such.
Sledgehammer should be good enough and faster but I live in a condo, and don't have a sledgehammer on hand so this method works for me.
The last time I dumped a pc I tore it apart, smashed every part, burned all in a giant oven, pack the remains in a box, drove down to the ocean side, rowed out about a mile and over the whole thing went and it all sank to the bottom, right next to Luka Brazzi