What, exactly, is deleted when you use the Clear and Delete? Does it totally wipe the HD, including the OS and image?

The reason I ask is that I have a 200-hour HD that I replaced, thinking that it was failing, but the problem turned out to be something else entirely. I would like to keep it as a spare to use in any of my 3 identical Directivos if one of them fails. I understand from reading here that when I do that I would have to use Clear and Delete after installing it, but what next? Will it just go into the guided setup, or is something else needed first?

Thanks