USB-IF Publishes USB 3.2 Specification Rated At 20 Gbps With Multi-Lane Operation
Subject: General Tech | October 3, 2017 - 12:00 AM | Tim Verry
Tagged: usb 3.2, usb-if, USB 3 Type-C, type c, usb
The USB Implementers Forum recently published and made official the specifications for the USB 3.2 standard first introduced in near-final form by the USB 3.0 Promoters Group back in July. The USB 3.2 standard specifies the physical and logical techniques for transferring data over physical USB cables (which are now all specified under their own standards decoupled from the USB 3.2 data transfer specifications) at up to 20 Gbps (~2 GB/s) using two 10 Gbps channels and the same signaling and 128b/132b encoding used by USB 3.1.
Like Thunderbolt, USB 3.2 takes advantage of multiple lanes to achieve the total bandwidth rather than trying to clock and run a single channel at twice the speed which is incredibly complex. In the case of USB 3.2, the specification defines two channels that can run 2 x 5 Gbps or 2 x 10 Gbps depending on the cable used with USB 3.1 Gen 1 (5 Gbps) or USB 3.1 Gen 2 (10 Gbps) cables respectively. In fact, users will be able to re-use their existing USB Type C cables to connect USB 3.2 hosts to USB 3.2 devices so long as they are up to spec. The USB-IF is able to achieve this by using the extra wire pairs in the Type C cables to enable the two lane operation. (5 Gbs cables would be upgraded to 10 Gbps speeds and 10 Gbps cables would be upgraded to 20 Gbps speeds when used with 3.2 hardware at both ends.)
The specification is expected to be finalized by the end of the year with USB 3.2 controllers and other hardware to begin production and roll outs in 2018. Devices supporting the faster USB 3.2 standard are expected as soon as 2019. Desktop users should get access first in the form of PCI-E add-on cards with new USB 3.2 controllers from third parties with native CPU and chipset support from AMD and Intel following in a generation or two (processor generation that is). Laptop and mobile users will have to wait until at least 2019 if not later for the faster standard to come standard.
It is interesting that they have decoupled the USB data transfer standard from the physical cable standards. It seems that USB Type C cables are the star of the show, but that cables like Type A and Micro cables are not going away and could be used with USB 3.2 with the caveat that you would need to buy new USB 3.2 cables which should be backwards compatible with older USB standards but current cables (SuperSpeed Type C cables being the exception) aren't forwards compatible--they might work but will support the higher speeds. At least that is my understanding of it. I am curious if Type C will be more prevalent with USB 3.2 or if we will still see motherboards with a single USB Type C nestled among many more Type A ports. I suppose the number of Type C vs Type A ports will all depend on how many new devices adopt Type C as the USB 3.2 physical interface of choice though, something we will just have to wait and see on! It is nice to see some competition for Thunderbolt though even at 20 Gbps USB 3.2 still lags behind the 40 Gbps of Thunderbolt 3 (20 Gbps with passive copper cables) which Intel is allegedly planning to make royalty free next year. USB 3.2 also has more overhead and is less ideal for things like external graphics. On the other hand, it may just be the cheap enough and fast enough connector that will get the design wins while Thunderbolt continues to be more of a prosumer and professional interface for the higher end and expensive motherboards, PCs, and end devices.
If you are interested in the new 20 Gbps USB 3.2 specifications, the USB-IF has provided a 103 MB zip file with several documents including a 548 page PDF of the new standard and a redline comparison between it and USB 3.1 among other related documents for developers.