Three speeds on one connector
USB4 uses the USB-C connector and comes in three speeds. Version 1.0 (2019) defined 20 and 40 Gbps. Version 2.0 (announced in 2022) added 80 Gbps in both directions, plus an optional mode that sends 120 Gbps one way and 40 Gbps the other. Consumer labels say what a port does: USB 20Gbps, USB 40Gbps or USB 80Gbps.
That label matters because the specification only requires hosts to support 20 Gbps, so a port marked USB4 and nothing else can be the slowest tier. At full link speed, ignoring overhead and the drive's own limit, 1 TB takes:
- 6m 40s at 20 Gbps
- 3m 20s at 40 Gbps
- 1m 40s at 80 Gbps
One link, several jobs
USB4 tunnels more than one kind of traffic over the same link: USB 3.x data, DisplayPort video and, if the port supports it, PCIe. They share the bandwidth. A dock that drives a monitor while you copy files from a drive splits the link between the two, so the drive doesn't get the full figure above.
PCIe tunneling is optional on hosts. That matters for external SSD enclosures and GPU boxes that rely on it, so check that the port lists it before you buy.
USB4 and Thunderbolt
USB4 is based on the Thunderbolt protocol specification that Intel contributed to the USB Promoter Group, and the USB-IF says it works with existing Thunderbolt 3 hosts and devices. Thunderbolt 4 and 5 are certified products with firmer minimums. Where USB4 leaves features optional, Thunderbolt requires them. A good USB4 port can match Thunderbolt on speed, but only Thunderbolt promises the whole feature set.
Cables and labels
- Look for the speed on the port and on the cable, like USB 40Gbps or USB 80Gbps.
- A USB-C cable made only for charging or USB 2.0 data can't carry USB4 speeds, even when both ends could.
- The USB Promoter Group's announcement of version 2.0 describes the 80 Gbps mode over existing 40 Gbps passive cables and newly defined 80 Gbps active cables.