Thunderbolt, reportedly the brainchild of Apple but developed by Intel, was created as a new interface for connecting peripheral devices to a computer. A Thunderbolt cable simultaneously transmits two signals: one DisplayPort signal with image data and also a CI-Express signal. That PCI-Express bus can be connected to various controller chips from peripheral devices, for example a PCI-Express to SATA controller for external hard drives.
Thunderbolt has a number of advantages over existing interfaces such as USB 3.0. Aside from transmitting image and other data through just one cable, you can also chain several Thunderbolt devices. This means that all your Thunderbolt devices can be connected by a single cable to your PC or laptop. A good example of this principle is Apple's Thunderbolt display. It's a monitor in which various controller chips have been integrated, including Gigabit LAN, Firewire and USB. All you need to do is connect the monitor with a Thunderbolt cable to your Apple laptop, and the rest of the devices will be connected as well.
The second advantage of Thunderbolt is the speed. Intel claims rates of up to 10GB/s or 1.5GB/s in both directions. That is more than the theoretical maximum of 480MB/s that USB 3.0 promises to deliver.
Thunderbolt uses the same physical connector as a Mini-DisplayPort. The interfaces are compatible, in the sense that you can connect a DisplayPort monitor to a Thunderbolt connector. Internally, however, Thunderbolt cables are different than DisplayPort cables. That means that it is not possible to use a DisplayPort cable for connecting a Thunderbolt hard drive, for example. Thunderbolt cables are also not particularly cheap.
Apple users have been able to enjoy the performance and user-friendliness of Thunderbolt for some time now, but with the introduction of the MSI Z77A-GD80, Thunderbolt is taking its first steps into the Windows environment. You can read the rest of MSI Z77A-GD80 preview on Hardware.info.