USB4 Technical Specifications


USB4 Technical Specifications

In March 2019, the USB Promoter Group (leader group) first released the USB4 specification, the next-generation USB architecture. In early September, the USB Promoter Group released the final USB4 specification standard.

USB4 has the following characteristics:

1. Maximum transmission speed of 40 Gbps

Through dual-channel transmission, the theoretical maximum transmission speed of USB4 should be 40 Gbps, which is the same speed as Thunderbolt 3 (hereinafter referred to as "Thunderbolt 3")

2. Compatible with Thunderbolt 3 interface

Some (but not all) USB4 devices are also compatible with the Thunderbolt 3 interface, which means that if you have a USB4 interface on your device, it is possible to also connect Thunderbolt 3 devices.


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3. Have dynamic bandwidth resource allocation capabilities

If you use the USB4 port as well as an external display and data transmission, this port will allocate the appropriate bandwidth according to the situation. For example, if video only needs 20% of the bandwidth to drive a 1080p display, the remaining 80% of the bandwidth can be used for other things. This was not possible in the era of USB 3.2 and before. Before this, the way USB worked had to take turns.

4.USB4 devices will all support USB PD

USB PD is USB Power Delivery, which is one of the mainstream fast charging protocols. This is also developed by the USB-IF organization. This specification can achieve higher voltage and current, and the power delivered can reach up to 100W. And can freely change the direction of power transmission.


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5. Only use USB Type-C interface

With this feature above, it is natural that we can also know that USB4 can only run through the USB Type-C connector. In fact, not only USB PD, but also other types of USB-IF standards only apply to Type-C.

6. Backward compatible with past protocols

USB4 can be used with USB 3 and USB 2 devices and ports. That is, it is backward compatible with previous protocol standards.

Of course, when a USB4 device is connected to a USB 3.2 port, it cannot transmit at 40 Gbps, and the old-fashioned USB 2 interface will not become faster because it is connected to the USB4 interface.


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7. What is the relationship with Thunderbolt 3?

In March of this year, Intel "donated" Thunderbolt 3 technology to the USB-IF organization, and the USB4 specification came out shortly thereafter. In fact, USB4 uses the Thunderbolt 3 protocol, and there is not much difference between the two.

8.About naming

This year's USB4 standard is "USB4", not "USB 4", without spaces. In this regard, Brad Saunders, CEO of USB Promoter Group, explained that the purpose of removing the spaces is to shift the focus from the version number to the brand name.

9. When is it available?

Although the current USB4 specifications have been released, it is almost impossible to see USB4 products on the market until 2020. According to Sanders, the typical development cycle for new products is 12 to 18 months.



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