Thunderbolt (originally codenamed Light Peak) is an interface for connecting peripheral devices to a computer via an expansion bus. Thunderbolt was developed by Intel and brought to market with technical collaboration from Apple Inc. It was introduced commercially on Apple’s updated MacBook Pro lineup on February 24, 2011, using the same port and connector as Mini DisplayPort.
Thunderbolt essentially combines PCI Express and DisplayPort into a new serial data interface that can be carried over longer and less costly cables. Because PCI Express is widely supported by device vendors and built into most of Intel’s modern chipsets, Thunderbolt can be added to existing products with relative ease. Thunderbolt driver chips fold the data from these two sources together, and split them back apart again for consumption within the devices. This makes the system backward compatible with existing DisplayPort hardware upstream of the driver.
Apple’s iMac 2011 showed that this compatibility is limited to the video output, as video input is incompatible with DisplayPort and mini-DisplayPort devices, and only allow Thunderbolt-equipped computers to send a video signal to 2011 iMac’s through Thunderbolt cables, exclusively, breaking compatibility with existing DisplayPort and mini-DisplayPort equipped computers.
The interface was originally designed to use flexible optical fiber cables, but a version using conventional copper wiring was also developed to furnish the desired 10 Gb/s bandwidth at lower cost. Intel’s implementation of the port adapter folds Thunderbolt and DisplayPort data together, allowing both to be carried over the same cable at the same time. A single Thunderbolt port supports hubs as well as a daisy chain of up to seven Thunderbolt devices; up to two of these devices may be high-resolution displays using DisplayPort. Apple sells existing DisplayPort adapters for DVI, dual-link DVI, HDMI, and VGA output from the Thunderbolt port, showing broad compatibility.