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This Tuesday, the USB developer forum has released the official specification of the USB4 protocol. If your initial reaction was "oh no, not yet," do not worry: the new specification is backward compatible with USB 2 and USB 3, and it uses the same USB Type-C connectors as modern USB 3 devices.
Connectors and cables
Although you can still connect standard devices with USB type A or USB type B connectors to new USB4 laptops and hubs, you will need to do so with dongles. Older non-reversible connectors are not capable of supporting USB Power Delivery, a smart charging protocol that allows faster (or slower, but less battery-intensive) charge rates to be negotiated.
This transition to USB Type-C should interest us all. Even if the power and data transmission features do not interest you, USB Type C adapters are much easier to connect. My family is destroying so many Micro-USB B charging cables I've seriously considered setting up a recurring monthly delivery on Amazon – but my eight-year-old son has not damaged a single C-type cable during eight months. The difference is huge.
Although existing USB 3.x charging cables continue to work properly, you will need to purchase new USB4 cables to take advantage of the full range of power and data solutions offered by the protocol.
(And in case you're wondering, the USB developer forum document puts spaces in "USB 2" and "USB 3", but not "USB4".)
Thunderbolt Compatibility
In 2017, Intel donated the Thunderbolt 3 specification to the USB Developer Forum for use by third parties. Thunderbolt is important because its incredibly high 40 Gbps signaling rate makes it possible to create externally connected peripheral GPUs as well as high-speed, low-latency connections to more traditional peripherals such as storage and displays. USB4 offers Thunderbolt 3 compatibility, but only if the manufacturers want it. Brad Saunders, CEO of the USB Promoter group, expects most computers to offer Thunderbolt 3 compatibility, unlike phones and tablets.
Another problem is that although the use of the standard is free of rights, the use of the mark is not. If manufacturers want to announce that their devices are compatible Thunderbolt 3, they must nevertheless be certified by Intel, which implies a hardware validation process decidedly not free. If Intel continues to require this direct validation to be able to use the Thunderbolt brand, new terms may appear to inform consumers of the presence or lack of compatibility with Thunderbolt 3 devices.
USB4 low, medium and high speed
All USB4 devices do not support the total 40 Gbps throughput of the specification. USB4 devices can be designed for signaling rates of 10 Gbps, 20 Gbps or 40 Gbps. There is unfortunately no indication of proposed clear mark, such as a physical port color change for high speed connections. Consumers will therefore have to look closely at the data sheets if they wish to benefit from the highest rates available.
The lowest transfer rate of USB4 equates to SuperSpeedPlus of USB 3.1, also at 10 Gbps. Its higher speeds of 20 Gbps and 40 Gbps require dual-channel cables; the 20 Gbps throughput will work with any type 2 dual-channel USB 3.2 cable, but the 40 Gbps throughput may require more expensive, 40 Gbps certified cables.
The protocol also specifies rate control for multiple devices connected to the same port. This means that more devices can be connected to a single port before significant latency and throughput issues arise. For example, a USB4 1080p display may announce a 3Gbps data requirement, which would be prioritized over other devices connected to the same port. This can prevent deletion of images or other latency issues with a storage device and a display connected via the same port and cable.
Fast charge for all
Some, but not all, of the current harvest of USB Type-C 3.2 devices support the USB-PD power supply protocol. This changes with USB4 because USB-PD support becomes mandatory for all devices. Intelligent charge rate negotiation brings both faster charging and longer battery life to the devices that support it. Energy-hungry devices, such as mobile phones and laptops, can charge up to 100 W, while less energy-hungry devices, such as headphones, can opt for a rate much lower maintenance charge, by saving the battery of laptops and by feeding the phones.
Conclusions and availability
The faster signaling speed of the USB4 is not likely to result in a sudden acceleration of everything. In particular, storage devices such as external disks and USB sticks will always be subject to the limits of their underlying media. It is not uncommon to see cheap 3.1 USB sticks exceeding 30 MB / s or less, which is even less than 480 Mbps USB 2.0 speed, not to mention the 5 Gbps speed of 3.1.
The Thunderbolt 3 expansion from some Intel peripherals selected – hopefully – from the majority of laptops and PCs is a welcome change, as does the mandatory support of the USB-PD.
The USB4 specification itself is available today, but we do not expect OEMs to deploy the first USB4 devices before 2020, with widespread availability more likely by early 2021.
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