With USB4 and USB 3.2, USB is more powerful and convoluted than ever


In recent years, the USB Implementers Forum (USB-IF) has developed this bizarre habit of releasing specification updates that are often tremendous steps forward but are obscured by confusing, misleading, or downright terrible naming. With the announcement of the USB4 (no space!) specification, the group has reached the apex of powerful features/confusing nomenclature.

USB4 is a big deal 

First, let us bask in the big news of the day: The USB-IF announced USB4, with no space between the "B" and the "4," cutting against all other USB naming schemes. Partially, that's no doubt because it's actually a new architecture, built on Intel's Thunderbolt protocol. Even so, it's compatible with Thunderbolt 3, USB 3.2, and USB 2.0. When an inferior-spec device is connected, a USB4 port will negotiate the "best mutual capability" of the two connected devices.

Thunderbolt 3 has been one of the (optional) crown jewels of USB Type-C, providing a blistering 40 Gbps theoretical bandwidth compared to USB 3.1 Gen 2's 10 Gbps. Now, the speed of Thunderbolt 3 becomes part of USB because Intel has allowed it to happen. Previously, companies implementing TB3 had to pay royalties to Intel because it was a proprietary technology. Now it's in the hands of the USB Promoters Group, thereby "enabling other chip makers to build Thunderbolt compatible silicon, royalty-free," according to an Intel announcement. Devices will still need a special controller on either end of the connection to take advantage of those delicious speeds, though. Not for nothing, upcoming 10-nm Intel chips will have native TB3 support. 

Also, USB 3.2

USB 3.2 has been kicking around since 2017, but recent stirrings at MWC 2019 indicate that we should be seeing the technology actually land on shipping devices soon. The presence of USB 3.2 has also further muddied the naming waters of the USB ecosystem. Like past USB 3.x updates, this one subsumes all of the changes and errata of the previous iterations, but it's big feature is a doubling of bandwidth.

USB 3.1 Gen2 can hit 10 Gbps, but it does so with a bus that has one Tx and one Rx; USB 3.2 uses a dual-bus architecture to double that to 20 Gbps. From the USB 3.2 specification document: "One bus is a USB 2.0 bus (see Universal Serial Bus Specification, Revision 2.0) and the other is an Enhanced SuperSpeed bus (see Section 3.1). USB 3.2 specifically adds dual-lane support."

Because any new USB 3.x subsumes the earlier USB 3.x specifications, the USB-IF prefers to categorize not by number (eg, USB 3.2, USB 3.1, and so on) but by speed. Looked at one way, that makes sense; USB 3.2 Gen 1 is 5 Gbps, USB 3.2 Gen 2 is 10 Gbps, and USB 3.2 Gen 2x2 is 20 Gbps. The "2x2" indicator makes it clear (ish) that we're talking about the two-way architecture, but you could make the argument that just calling it "Gen 3" would be simpler. Alas. 

Ports' importance

Let us not forget that titles like USB 3.2 and USB4 don't necessarily tell you what physical ports (eg, USB Type-A or USB Type-C connectors) are in play, nor other capabilities like Power Delivery. So, consumers need to understand that although technically "USB 3.2" runs over USB Type-A or USB Type-C, you'll only get the full performance of USB 3.2 Gen 2x2 over a USB Type-C cable. 

Essentially, then, the emergence of USB 3.2 and USB4 mark a huge push away from USB Type-A ports towards USB Type-C ports. The future is a two-way USB street; USB 3.2 gives us 20 Gbps and USB4 gives us 40 Gbps over USB Type-C. USB Type-A is stuck at 10 Gbps, no matter what name you slap on it. 

That has ramifications for the way companies built their products. Presently, manufacturers have often been loading up their devices with both USB Type-A and USB Type-C ports to accommodate both legacy devices and more powerful ones. It's likely that will continue for years to come, but perhaps with an increasing percentage of USB Type-C to USB Type-A. But it seems the days of USB Type-A ports are numbered.

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