What it is and the problem it solves
Thunderbolt is the brand name of a hardware interface for connecting external peripherals to a computer. Intel developed it in collaboration with Apple, and it was first marketed as Light Peak. It first sold in an end-user product on 24 February 2011. It combines PCI Express and DisplayPort into two serial signals and provides DC power through one cable, with up to six peripherals supported from a single connector.
How it works
Thunderbolt controllers multiplex data lanes from PCI Express and DisplayPort devices onto two duplex Thunderbolt lanes, then separate them again at the other end. In the first generation each of the two duplex lanes runs at 10 Gbit/s, with one lane for input and one for output. A single port reaches up to six devices through hubs or daisy chains. A DisplayPort monitor without daisy-chaining support must sit at the end of the chain.
The interface was first meant to be purely optical. Intel found that copper wiring could supply 10 Gbit/s per channel at lower cost, and copper can also carry power. Thunderbolt 1 and 2 use the Mini DisplayPort connector; Thunderbolt 3, 4 and 5 use USB-C.
What works
Speed rose with each generation. Thunderbolt 1 ran at 10 Gbit/s. Thunderbolt 2, in 2013, joined the two channels into one logical 20 Gbit/s channel. Thunderbolt 3, in 2015, doubled that to 40 Gbit/s, supported two 4K displays at 60 Hz, and carried up to 100 watts of power over USB-C. Thunderbolt 4, specified in 2020, set a minimum PCI Express bandwidth of 32 Gbit/s, added direct memory access protection and supported hubs as well as daisy chains. Intel previewed Thunderbolt 5 in September 2023 at 80 Gbit/s symmetric, with up to 240 W of charging power.
Backward compatibility is wide. Thunderbolt 1 and 2 devices connect to later ports through passive adapters if they do not draw bus power, and Thunderbolt 4 and 5 ports accept Thunderbolt 3 devices.
What does not
Thunderbolt began as a niche port with poor support outside Apple’s devices. The USB Implementers Forum refused to allow a combined USB and Light Peak port. Optical cables cannot provide power, and the first of them, from Sumitomo Electric in 2013, sold almost only in Japan at 20 to 30 times the price of copper cables.
Compatibility has limits. Thunderbolt 4 and 5 devices do not work with Thunderbolt 1 or 2 hosts, even with an adapter. Newer Intel firmware on Windows disabled Thunderbolt 1 and 2 support over security concerns. Before March 2019 no AMD computers shipped with Thunderbolt, because Intel did not certify non-Intel platforms. At 80 Gbit/s, active cables that worked for earlier generations do not reach the new speed.
What it changes
Adopting USB-C for Thunderbolt 3 brought wider market acceptance. Intel announced in 2017 that Thunderbolt 3 would become royalty-free, and its specification went to the USB Implementers Forum on 4 March 2019. The USB4 specification, released on 29 August 2019, is based on the Thunderbolt 3 protocol and supports 40 Gbit/s. USB4 devices that carry PCI Express can be released without Thunderbolt certification, but may not use Thunderbolt branding, so rival devices can do the same job under different names. Intel retains control of Thunderbolt certification.
Is it worth your time
Yes, if you connect fast storage, high-resolution displays or docks and want one cable for data, video and charging. Thunderbolt 3 and later work over USB-C and accept USB devices. Because USB4 devices can carry PCI Express without Thunderbolt certification, check which standard a device names.
