USB4 spec promises Thunderbolt 3 support, 40Gbps bandwidth
6 March 2019 | 0
Meet USB4, which promises to simply the USB naming scheme and integrate the high-bandwidth Thunderbolt 3 specification. Just a week after the upcoming USB 3.2 specification’s branding scheme threatened to confuse PC buyers, the next USB spec is trying to resolve it all.
Though we don’t know the answer to all of the questions yet, it’s not too early to start thinking about USB4 as a combination of USB, the high-speed Thunderbolt 3 specification, and the convenient USB-C connector.
Cutting the confusion
If you have a cable connecting your PC to a peripheral, chances are that it’s USB. Over its 20-plus years of existence, the USB interface has continued to add new speed tiers, including USB 2.0, USB 3.0, and USB 3.1, while remaining backward-compatible with older versions. A USB-C port has also been created alongside the older USB-A port, in a bid to simplify the connector scheme. USB4 will use the USB-C port, and run at 40Gbps—about double the speed of the preceding USB 3.2 specification.
You probably won’t see USB4 hardware in the near future, however. The USB 3.2 specification was published in 2017 and is due to show up in products this year. USB4 is just a specification at the moment, and it hasn’t even been published. The publication date is scheduled for sometime in mid-2019, which means we won’t likely see USB4 hardware until 2020 or beyond.
There is also a separate, but related issue: To facilitate the transition, Intel said that it would follow up on a 2017 promise to contribute the Thunderbolt specification to the USB Promoter Group, the same organisation that announced the USB4 specification. Doing so will enable other chip makers in the USB-PG to build Thunderbolt 3 silicon royalty-free.
From a technical standpoint, USB4 is good news, promising to take the small jumble of USB specifications, form factors, and branding and consolidate them into something more understandable for a general audience. The timing of it all is a bit suspicious, given the backlash about the USB 3.2 branding scheme. But as the inventor of Thunderbolt, Intel wants to see the technology become more popular, too.
Many USB4 answers will have to wait
From Intel’s perspective, the timing is right to make Thunderbolt (even more) mainstream. Intel’s vision of one cable to rule them all was suspect when Intel announced Thunderbolt in 2015 — in part because that was supposed to be USB’s role. Since then, however, it’s become more accepted. According to Intel, more than 400 PC designs ship with Thunderbolt ports, as well as virtually all of the latest Apple Macs. About 450 peripherals have also been designed around Thunderbolt, Intel said.
What is unclear about USB4 is whether everything in Thunderbolt 3 will carry over: connecting a pair of 4K monitors at 60Hz using DisplayPort, peer-to-peer networking, and more. “Multiple data and display protocols” is how the USB Promoter Group describes USB4’s capabilities. In an interview, Jason Ziller, general manager of the Client Connectivity Division at Intel, didn’t go much further.
“It’s definitely designed to simplify things,” Ziller said, while declining to go into the exact specifications.
Basically, many of the questions enthusiasts want answers to cannot be clarified until the actual specification is released later this year. What is clear is that Intel isn’t relinquishing its hold on Thunderbolt, or on certifying compatible devices. “Thunderbolt as a solution, as a certification program, is retained within Intel,” Ziller added.
Some political questions, resolved
Politically, the move by the USB-PG isn’t as straightforward. The USB 3.2 branding controversy emanated from the USB Implementers Forum, essentially the marketing arm of the USB Promoters Group. The guidelines issued by USB-IF assigned confusing marketing terms to the various flavours of USB. USB4 has yet to be assigned any marketing terms.
It’s the USB-PG that comes up with the spec itself, including the original USB 3.2 specification that was released in 2017. The USB-PG is made up of Apple, Hewlett-Packard, Intel, Microsoft, Renesas, ST Microelectronics, and Texas Instruments. It’s to these companies that Intel will release the Thunderbolt protocol spec.
Originally, the implication was that a company that was not a member of the USB-PG would be unable to adopt the Thunderbolt specification or USB4. An Intel spokeswoman said Tuesday that that isn’t true.
“Intel has released the Thunderbolt protocol specification to the USB Promoter Group and its contributors,” the Intel spokeswoman said in a statement. “The royalty-free license to both the Thunderbolt protocol specification and the USB4 spec will be made available to anyone once the USB4 specification is released later this year. Access is not exclusive to the USB Promoter Group member companies.”
That would theoretically allow AMD or any other company to build in direct support for Thunderbolt into their processors, as Intel announced at CES in January: specifically, build Thunderbolt 3 support into “Ice Lake,” the CPU Intel will deliver by the end of 2019.
We still do not know the answers to other key questions: whether USB power delivery will be upgraded from its current 100W limit, for example, or the length of supported USB cables, or whether those cables will be color-coded to ensure compatibility, or what prices will be, and so on. The message, though, seems to be this: yes, USB is sort of a mess right now, but USB4 will (hopefully) simplify it all.
IDG News Service