What Is The Thunderbolt Port?
The Thunderbolt Port will support displays, hard drives, and other high-end devices through a single port, small port. It's faster, smaller, and features far more power than a USB or FireWire port. In fact, Thunderbolt is up to 20 times faster than USB 2.0 and 12 times faster than FireWire 800.
As for the Mini DisplayPort, Thunderbolt is the same exact size, so it's backwards compatible with all devices connected through the Mini DisplayPort.