The USB4 Specification

What distinguishes the USB4 technology?

Smart relationship with Thunderbolt™ 3

The USB4 specification was released in fall 2019 and is the successor to USB 3.2 as well as Thunderbolt™ 3. In order for USB4 to benefit from Thunderbolt™ 3 features and be compatible with Thunderbolt™ 3 (devices), Intel provided the Thunderbolt™ specification to the USB-IF (USB Implementers Forum) in 2019. The previously Thunderbolt™-specific ability to support various other protocols, such as DisplayPort, PCI Express, and even host-to-host transfers, is something USB4 inherited from Thunderbolt™, which is one of its major advantages over USB 3.2. The different data are "tunnelled", i.e. they are transmitted in packets over the same data line.

An USB4 connector in 3D view

Differences to Thunderbolt™ 3

USB4, like its predecessors, continues to work with the USB's own hub structure, so it has not adopted daisy-chaining from Thunderbolt™. Unlike Thunderbolt™, USB4 can be used license-free by hardware manufacturers, which is why USB4 devices are comparatively cheaper. USB4 supports the new DisplayPort 2.0 Alt Mode, which enables monitor resolutions up to 8K 60 Hz and HDR10.

Intelligent allocation of ressources for data flows

An important advantage of USB4 is the efficient, intelligent share of bandwidth. Previously, the bandwidth was divided equally between two lanes (= data streams), so 50 % of bandwidth per lane. Now the data streams are distributed with a much higher degree of compression (= granularity). If data and videos are transferred at the same time, USB4 can efficiently allocate ressources depending on requirements. That means optimized operation of data flows, because data are intelligently condensed, summarized or aggregated as required.

Doubled data rate possible

Another property inherited from Thunderbolt™ 3 allows doubling previous bandwidth in the ideal case. Now a maximum data transfer rate of 40 Gbps is achievable, provided all devices and cables or adapters involved support the USB4 Gen 3x2 specification. The following maximum data rates apply:

  • USB4 Gen 2x1 = 10 Gbps
  • USB4 Gen 2x2 = 20 Gbps
  • USB4 Gen 3x2 = 40 Gbps

Hot plugging und power supply

Peripherals can be connected, configured, used and disconnected while host and further peripherals are in operation. Up to now, the USB Power Delivery (USB PD) specification for charging also bigger devices, such as notebooks, was only supported by some USB Type-C ports. With USB4, USB PD is supported up to 100 Watts (5 A / 20 V) with "Standard Power Range", or up to 240 W (5 A / 48 V) with "Extended Power Range". Now, power for charging or operating the battery can be transferred between the host and peripherals in both directions.

Proven design

The construction method remains as physical as before, which should please not least the consumer. USB4 cables, plugs, and jacks are exactly the same design and appearance as USB Type-C™, even though the underlying technology has been enhanced.

USB4 - characteristics at a glance

  • Support of different data and display protocols (incl. DisplayPort and PCIe)
  • Intelligently shared use of total bandwidth depending on transfer requirements by tunnelling the data = a.o. for better video performanceg
  • Operation via two lane cables with data rate up to 40 Gbps (if certified 40 Gbps cables are used)
  • Downwards compatible to USB 3.2, USB 2.0 and Thunderbolt 3
  • USB Type-C™ connector used by default

Maximum data transfer rates USB versions

Version Lanes Data rate
USB 3.2 Gen 1 1 5 Gbps
USB 3.2 Gen 2 1 10 Gbps
USB 3.2 Gen 1x2 2 10 Gbps
USB 3.2 Gen 2x2 2 20 Gbps
USB4 Gen 2x1 1 10 Gbps
USB4 Gen 2x2 2 20 Gbps
USB4 Gen 3x2 2 40 Gbps

Post-question: Does every USB4 device provide Thunderbolt™ 3 compatibility?

Manufacturers can implement Thunderbolt™ 3 support in the USB4 specification, but are not required to do so - only USB4 hubs must be compatible. Thus, a USB4-capable device may end up not being compatible with Thunderbolt™ 3. For the consumer and buyer, this means that they should take a close and thorough look at the specifications of the respective device before buying it - if they value Thunderbolt™ 3 compatibility. Manufacturers can implement Thunderbolt™ 3 support in the USB4 specification, but are not required to do so - only USB4 hubs must be compatible. Therefore, it may happen that a USB4 able device is finally not compatible with Thunderbolt 3. That means for the customer and buyer to exactly and thoroughly check the specifications of appropriate device before purchasing – given he / she / it attaches importance to Thunderbolt 3 compatibility.

Tip: Product presentation USB4 External Enclosure from Delock