Are you one of those people who needs to know how things work? If you're not, then you can move along to the next post, as this will, most likely, not interest
Still here? Good. Here's a piece that details the terribly secret, or at least previously secret, bootcode of the Xbox. How it does what it does. It's a fascinating insight into exactly how the Xbox, by default, stops you running backups/copies, or homebrew software. Oh yeah, and a little OS called Linux.
May make your head hurt a bit though.