Originally Posted by jbcohen
I also learned the difference between an external HDD used for desktops and those that are used for porting data with you. The difference being that the portable ones require only one connection, a USB port. The ones ment for HD backup require both the USB and an electrical connection.
I think that mostly just has to do with the power consumption of the drive. I've noticed that some of the ones that require only a USB will require two USB connections to provide enough power to the drive. They usually try to engineer portable drives to minimize these constraints, but it all boils down to drive efficiency. i.e., a Hitachi HD will need less power than a WD Raptor.