The USB Implementers Forum (USB-IF) has just published the official specifications of the new USB4 standard (without spaces between name and number). The objective is to build around the existing system (currently USB 3.0, 3.1, and 3.2) to add new functions and increase throughput.

A better distribution of bandwidth

In addition to doubling speeds, USB4 differs from USB 3.2 in its dynamic bandwidth management, between several protocols used on the same bus. It, therefore, gains in intelligence compared to the system of dividing the bandwidth into equal parts. It may be particularly effective for data and video transmission, for example, when connecting a 4K monitor and an external SSD. Video transmission (HDMI and DisplayPort) is part of the USB Type-C specifications but was not yet optimally managed when bandwidth is shared with data. Also, all USB4 devices must be compatible with the Power Delivery standard, which allows the USB Type-C to be used for power supply (up to 100 watts in theory).

Thunderbolt 3 interface is optional

It will still be possible to use your old USB 2.0, 3.0, 3.1, and 3.2 devices. However, if the Thunderbolt 3 interface is included in the specifications, it is not mandatory. The USB-IF justifies this choice by indicating that some manufacturers will not require the functions of the Thunderbolt 3 interface in their devices with USB4 connectors, for example in the case of smartphones. This choice of USB-IF is all the more paradoxical as USB4 was mainly designed from the Thunderbolt 3 interface, which Intel “offered” to USB-IF. Thus, manufacturers who will use USB4 will not have to pay royalties to Intel.

The characteristics of this new standard

The main features of USB4 are as follows:

  • Data rates up to 40 Gbit/s (Gen 3 x 2 mode)
  • Dynamic bandwidth management
  • Compatibility with Thunderbolt 3, USB 2.0, and USB 3.2 interface
  • Use of existing USB Type-C cables

USB4, therefore, doubles the data rates compared to USB 3.2 (20 Gbit/s in Gen 2 x 2 mode) and quadruples them compared to USB 3.1 (10 Gbit/s in Gen 2 mode). The USB4 will also be able to operate in 10 Gbit/s and 20 Gbit/s. Therefore, it will be necessary to read the characteristics of the device to know if the 40 Gbit/s are present or not. Note that the interface will only work with USB Type-C connectors, a requirement already introduced with USB 3.2. Besides, speeds of 40 Gbit/s can only be achieved with certified Type-C USB cables. It may, therefore, be necessary to buy new cables to benefit from it.

Logos and designs are not yet defined

While USB4 has many advantages, the new specifications may still create confusion for users.

For example, the USB-IF has not yet specified how speeds will be indicated and which logos will be used on connectors and cables. The situation is already complicated at the moment, as it is challenging to know which USB 3.x is used when looking at a computer’s USB Type-C connector. Finally, we will have to be patient because the first devices with USB4 ports are not expected until next year, or even in 2021 if the manufacturers are not in a hurry…