Stefan Mileschin

Thunderbolt is Intel’s high-bandwidth, do-everything connector, designed as a potential future path for all things external to a system - displays, USB devices, external storage, PCI Express, and even graphics cards. The first version of Thunderbolt supported up to 10Gb/s bandwidth (uni-directional) for each port (double that of USB 3.0, but at a much higher implementation cost). Thunderbolt 2 doubled the bandwidth to 20 Gbps per port (bi-directional) by combining the four 10Gb/s channels into two 20Gb/s channels, thus enabling support for 4Kp60 raw video transfer (which may need up to 15 Gbps). Motherboards with Thunderbolt 2 certification started rolling out in the second half of 2013, but peripherals capable of taking advantage of Thunderbolt 2 were quite rare.

http://www.anandtech.com/show/7936/g...rbolt-2-lineup