[quote name='Salamando3000']Now, I could be mistaken, but External means it can run off usb power, while Desktop requires an ac adapter (or something similar) to power it, making it a lot less portable. Besides, I don't think target sells internal HD's....or at least I've never seen 'em.[/QUOTE]
The wording in the add is a little misleading. It says that the 500GB drive is portable, which means that you'll need two USB ports, one for data and one for power. For the 1TB, it says "desktop" which sounds to me like an internal, 3.5" drive, but it could also be an external drive that requires an AC adaptor.