USB 4 announced days after USB 3.2: Here's what you need to know

USB 4 is built on top of Intel's Thunderbolt 3 specification, but isn't expected to be in products until at least 2020. USB 3.2 is intended to bridge the gap, but suffers from terrible naming.

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The full USB 4 specification is expected to be formally published "around the middle of 2019," according to a press release from the USB Promoter Group on Monday. USB 4 is based on Intel's Thunderbolt 3 specification, allowing USB 4 to reach speeds of 40 Gbps, doubling the bandwidth of the USB 3.2 specification announced last week.

In 2017, Intel pledged to open Thunderbolt 3 to the industry under a royalty-free license, paving the way for USB Promoter Group and USB-IF to adopt the technology for the next generation of USB standards.

Notably, Thunderbolt 3 itself supports PCIe 3.0 and DisplayPort 1.2 signaling, making it capable of driving 4K monitors at 60Hz, as well as external GPUs to boost the graphical capabilities of notebook PCs and small form factor computers like the Mac Mini. Actually achieving 40 Gbps transfer on Thunderbolt 3 is more complex than it may appear at first glance, as "active" cables with circuitry in the connectors are required for cables longer than 50 cm (1.5 ft).

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How this will be handled in the USB 4 specification is yet to be seen, though the press release mentions "40 Gbps-certified cables." The practical utility of making the bus universal, but relying on application-specific cables is questionable. For the uninitiated, it would easily be more confusing than the color-coding industry standard adopted decades ago.

With the formal specification expected in the middle of this year, systems actually shipping with USB 4 are unlikely to appear before 2020. Given that Thunderbolt 3 is a known quantity, the learning curve for system designers is likely quite low, though the silicon needed to deliver it for servers, desktops, and laptops will take time to reach the market.

USB 3.2: Coming soon, to a computer near you

The USB 3.2 specification was formally published in 2017, though the final standards for naming were published in late February to universal condemnation, due to the unnecessary retroactive renaming of previously published standards and painfully poorly thought out branding decisions made by the USB-IF.

USB 3.2 will double the speeds over USB-C to 20 Gbps, prompting the USB-IF to label this technology "USB 3.2 Gen 2x2," in an apparent war against common sense. With the availability of USB 3.2, the naming convention is to be updated as follows:

USB generation
Previous nameNew nameSpeedTypeBrand name
USB 3.0USB 3.1 Gen 1USB 3.2 Gen 15GbpsUSB-A/CSuperSpeed USB
USB 3.1USB 3.1 Gen 2USB 3.2 Gen 210GbpsUSB-A/CSuperSpeed USB 10Gbps
USB 3.2NoneUSB 3.2 Gen 2x220GbpsUSB-CSuperSpeed USB 20Gbps

Devices with USB 3.2 are expected to hit the streets later this year. According to ZDNet's Liam Tung, "Fortunately for consumers, USB-IF is encouraging device makers to stick to the SuperSpeed nomenclature."

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Image: Josh Miller/CNET