Important: When a Thunderbolt 3 port is actually running in Thunderbolt mode rather than as a basic USB port or DisplayPort video output, the only data types that are running across the Thunderbolt link are DisplayPort and PCIe.
The upcoming USB4 spec will switch to a dynamic bandwidth allocation model like Thunderbolt. This is in contrast to using regular USB-C for both DisplayPort and USB 3.x simultaneously, where each signal type is allocated two lanes, regardless of how much bandwidth they need at any given time. This means Thunderbolt makes efficient use of available total bandwidth since the PCIe/DisplayPort composition of the Thunderbolt signal can be adjusted dynamically.
Note that when Thunderbolt is in use, all four high speed lanes in the USB-C connector are tasked with carrying a "Thunderbolt signal", which consists of PCIe and DisplayPort multiplexed together. PCIe support is mandatory for Thunderbolt 3 – at least a PCIe x2 interface, with a PCIe x4 interface being optional in the spec. PCIe – This is only available on USB-C ports that support Thunderbolt 3 and when running in Thunderbolt 3 mode.In a Thunderbolt connection, DisplayPort would be multiplexed with PCIe, more detail below. When using something like a USB-C dock that wished to support video and USB 3.x data, only two lanes would carry video since the other two would be allocated to USB 3.x – and consequently you’d have half the video bandwidth available compared to the USB-C to DP cable scenario. When using something like a USB-C to DisplayPort cable, all four lanes would carry video. DisplayPort can be run either within a Thunderbolt signal or as regular DisplayPort traffic, and it also uses the high speed lanes in a USB-C connector. DisplayPort – Support for DisplayPort over USB-C, technically referred to as “DisplayPort Alt Mode”, is also optional on USB-C ports, but is mandatory on all USB-C ports that support Thunderbolt 3.The other two remain unused, at least as of USB 3.x Gen 1 and Gen 2 (5 Gbps and 10 Gbps, respectively.) USB 3.x – Support for USB 3.x is technically optional, but when available, a USB 3.x device plugged into a USB-C port would use two of the four “high speed lanes” in a USB-C connector.USB 2.0 – USB-C connectors contain dedicated pins for USB 2.0 traffic.
Since Thunderbolt 3 presents some unique security considerations, and there are now several different “security levels” for a system's Thunderbolt 3 controller that can be configured in the system’s BIOS setup, I thought I’d write an explainer for anyone who might be confused about or simply interested in the differences.įirst, it’s important to understand that a USB-C port that supports Thunderbolt 3 can carry different types of data traffic, since this will be relevant to what will or will not work under various security modes and why.