USB 4 version 2.0 | What’s new in the world’s fastest USB

In August 2022, the USB Promoter Group, an association of major companies responsible for developing new USB standards, announced USB 4 version 2.0. As the name implies, this is the second generation of high-speed connection for computers, mobile phones and other devices.

The protocol’s biggest innovation is a connection speed of up to 80 Gbps, making it the fastest version in the world — even surpassing Intel’s 40 Gbps Thunderbolt 4, which has long been considered the benchmark — but there are more new features that promise to entice those who were still apprehensive USB 4, especially professionals who rely on Thunderbolt ports.

Features of USB 4 version 2.0

Following the standard adopted with the original version, USB 4 version 2.0 uses USB-C connections and is backward compatible not only with USB 4 version 1.0 itself, but also with USB 2.0, USB 3.2 and Thunderbolt 3. However, unlike its predecessors, the new standard uses hardware-level tweaks to deliver double the speed, reaching 80 Gbps.

For the benefit of users already using Thunderbolt and USB 3.2 Gen 2×2 protocols, with transfer speeds of 40 Gbps and 20 Gbps, the new standard will also take advantage of USB cables prepared for these connections, while receiving special certified models that provide 80 Gbps.

Updated PCI Express and new USB 3.2 tunneling

Along with the speed increase, USB 4 version 2.0 updates several other technologies integrated into the protocol, highlighting support for PCIe 5.0, increasing the bandwidth available for accessories such as external GPU (eGPU) and high-performance USB hubs, in addition to DisplayPort 2.0.

For this, the connection will use a turbocharged version of the tunneling technology (packaging data to send) in the USB 3.2 protocol. By default, using the USB 3.2 Gen 2×2 version, these ports can deliver the same 20 Gbps for tunneling, which ultimately limits bandwidth-intensive applications such as eGPUs themselves.

Devices such as eGPUs are among the main users of the USB 3.2 advanced tunneling present in USB 4 version 2.0 (Image: Disclosure/Gigabyte)

With the new version of USB 4, these peripherals will be able to exceed the standard bandwidth, providing support for more monitors, or higher resolution screens, and even more performance for eGPUs — this type of device usually provides well below what the hardware is capable, precisely because of the speed limit.

According to the USB Promoter Group, USB 4 Version 2.0 is designed specifically for users who tend to use a single port to connect multiple devices, a feature that can be seen in the high speed the standard provides, and is not very useful for consumers who demand less from a computer.

A speed of 120 Gbps is technically possible

Highlighted for delivering high speeds and supporting the Thunderbolt standard, USB 4 version 1.0 achieves transfer speeds of 40 Gbps using 4 communication lanes in a symmetrical configuration identified as 2 Tx + 2 Rx. Each lane has 20 Gbps, providing the bandwidth needed to achieve the specified speed.

However, by using PAM-3 coding, which adds an extra bit of information to the signal, it is possible to increase the limit to 80 Gbps. Interestingly, USB 4 version 2.0 may adopt a similar strategy to achieve 120 Gbps, at least in theory — USB 4 version 2.0 specifications are still under development and are not expected to have a full feature list until 2023.

Using an asymmetric configuration of communication lanes, USB 4 version 2.0 can theoretically achieve speeds of up to 120 Gbps (Image: Envato/puhimec)

The indication comes from the documentation of Keysight, a company specializing in the development of devices for testing and verifying protocols. The device dedicated to confirming USB 4 version 2.0 supports the organization of asymmetric communication paths called 3 Tx + 1 Rx, in which the host (computer, tablet, PC) can send data at a speed of up to 120 Gbps, while the peripheral device (eGPU, USB hub) would maintain speeds of 40 Gbps for communication.

Using the DisplayPort 2.0 UHBR20 signal, this bandwidth would be enough to support monitors with resolutions up to 8K @ 85 Hz without compression or up to 8K @ 144 Hz with compression, while still maintaining 40 Gbps for communication with other accessories, such as hubs , cameras, storage drives and more.

Source: USB Promoter Group, Tom’s Hardware

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