USB4 is a specification by USB Implementers Forum (USB-IF), which was released in version 1.0 on 29 August 2019. The USB4 protocol is based on the Thunderbolt 3 protocol; the Thunderbolt 3 specification was donated to the USB-IF by Intel Corp. The USB4 architecture can share a single high-speed link with multiple end-device types dynamically, best serving each transfer by data type and application.
In contrast to prior USB protocol standards, USB4 requires USB-C connectors, and for power delivery, it requires support of USB PD. USB4 products must support 20 Gbit/s throughput and can support 40 Gbit/s throughput, but due to tunneling even nominal 20 Gbit/s can result in higher effective data rates in USB4, compared to USB 3.2, when sending mixed data. In contrast to USB 3.2, it allows tunneling of DisplayPort and PCI Express.
Support of interoperability with Thunderbolt 3 products is optional for USB4 hosts and USB4 peripheral devices, and is required for USB4 hubs on their downward facing ports and for USB4-based docks on their downward and upward facing ports. On the other hand, support for USB4 is required in Thunderbolt 4.
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