64bit Vista is using over 20gigs

I just installed 64bit home premium on my secondary 80gig hard drive, I have a 320gig also but I usually just keep all my junk/downloads on that so if I have to reinstall windows I pretty much only have to wipe out the 80gig with barely nothing on it.

Anyways, this is my first time using a 64bit OS....and I'm already noticing little differences. There are parts of Windows that weren't there before, and there are things that are actually missing from 32bit Vista.

But with just the OS installed on that 80gig, I only have 50.4gb left out of 74.5...and the Windows folder is only using up around 12gigs, so I don't get it, where did that other 10+ gigs go?