Thunderbolt is a high-speed I/O interface that was developed by Intel and was introduced by Apple in 2011. It is based on the PCI Express and DisplayPort technologies and supports both data devices and displays.
Since Thunderbolt is based on the PCI Express architecture, external devices connected via Thunderbolt can achieve performance that was previously only possible from internal components. Additionally, the Thunderbolt interface offers 10 Gpbs of throughput in both directions. That is more than 12 times as fast as Firewire 800 and over 20 times faster than USB 2.0. While a FireWire 800 interface can only support one stream of 720p video, a Thunderbolt interface can support 8 simultaneous 720p video streams.
Like USB and FireWire, Thunderbolt can provide power to connected peripheral devices. That means external devices that require 10 watts of power or less can be powered directly from the Thunderbolt port. Additionally, simple adapters can be used to connect USB, FireWire, and Ethernet devices to a Thunderbolt port.
While Thunderbolt is primarily used as a high-speed data interface, it can also be used to connect high-resolution displays. The Thunderbolt interface is physically identical to the Mini-DisplayPort interface and therefore can be used to connect a DisplayPort monitor. Like HDMI, DisplayPort supports both audio and video, eliminating the need for a separate audio cable.
Thunderbolt devices can be daisy-chained, meaning multiple devices can be connected in sequence to a single Thunderbolt port. For example, you can connect a Thunderbolt display to a computer and a Thunderbolt external hard drive to the display. You could also connect a second Thunderbolt monitor to the first display. This means you can connect two external displays to a laptop, as long as the laptop supports the resolution required for two screens.