All Things USB 3.1 And USB Type-C: An Explainer

Over the last year or so, there have been many developments in the USB space, and although the official specifications haven't changed, we've consolidated and explained all the helpful information around USB 3.0, both versions of USB 3.1, and the USB Type-C connector.

When USB 3.1 became common knowledge last year (even though it was actually released in 2012), there was some confusion. USB 3.1 was gaining attention about when the USB Type-C connector first appeared, so it's easy to understand how the two would be conflated. However, they're not the same thing. One is a data transfer protocol, and one is a type of connector. Another way of thinking of it is that Type-C is the pipe, and USB is (one of) the things that can flow through the pipe.  

There is further clarification needed around other aspects of USB 3.1 and USB Type-C, though. A year past our last article on the subject, we spoke at length with the USB Implementer's Forum (USB-IF) to craft a primer, if you will, about all things USB and Type-C.

What's The Deal With USB 3.0, USB 3.1 Gen1, And USB 3.1 Gen2?

It's important to parse out the differences between USB 3.0, USB 3.1 Gen1 and USB 3.1 Gen2.

There are two types of USB 3.1: There's a Gen1 and a Gen2, and they offer different data transfer speeds. Both USB 3.0 and USB 3.1 Gen1 can transfer data at speeds up to 5.0 Gbps (8b/10b encoding), whereas USB 3.1 Gen2 can transfer data at speeds up to 10 Gbps (128b/132b encoding).

USB 3.0 and USB 3.1 Gen1 are actually the same thing -- almost. Simply put, USB 3.1 Gen1 is USB 3.0 plus all of the changes that have been made to USB 3.0 over the years. According to the USB-IF's documents, these changes include "added performance boosts to meet requirements for USB storage, display and docking applications," as well as USB 3.0 Engineering Change Notices (ECNs).

"The USB 3.1 specification absorbed USB 3.0, meaning the terms USB 3.0 and USB 3.1 Gen 1 are synonymous," a USB-IF representative told Tom's Hardware. "By incorporating USB 3.0, we're reducing the number of documents a developer needs to reference (we're talking hundreds and hundreds of pages of technical documents that developers have to parse through) and including all relevant information to ensure products are properly developed to be backwards compatible (protocol-wise, not related to cables/connectors)."

The answer to the question that just popped into your head is no, there's no reason to market anything as "USB 3.0" at this point.

In order to clarify which is which and what is what, the USB-IF has turned to branding.

A Branding Issue

You may have never even seen an OEM specify "Gen1" or "Gen2" in marketing materials mentioning USB 3.1. Partially, this is because the USB-IF uses specific branding to clarify which USB 3.1 is which. USB 3.1 Rev1 (5 Gbps) is called "SuperSpeed USB," and USB 3.1 Rev2 (10 Gbps) is called "SuperSpeed USB 10 Gbps." Note that on the actual logos, these appear as "SuperSpeed" and "SuperSpeed+," respectively. (What's in a "+" sign? Double the data speed, that's what.)

This emphasis on branding has become of particular import in the wake of the launch of USB 3.1 and USB Type-C, as well as the rise of the USB Power Delivery spec. (USB PD is actually its own standard, apart from the data performance aspects of USB 2.0 and USB 3.1.) One could argue that the launches necessitated it, as not only are there multiple versions of USB 3.1 that require clarification, USB Type-C is a much more flexible connector (pun not intended) than older USB standards, and USB PD is another wildcard; in other words, the mere presence of a Type-C port on a device tells you little about what that particular port can do.

Instead, you should look for the branding in order to be able to tell what a port is capable of. Here it is in a handy table:

USB 3.1 Gen1 with USB Power Delivery (USB PD)N/AN/A

USB 3.1 Gen2SuperSpeed USB 10 Gbps

USB 3.1 Gen2 with USB Power Delivery (USB PD)N/AN/A

USB 3.1 Gen 2 with DisplayPort over Type-CN/AN/A

USB 3.1 Gen 2 with DisplayPort over Type-C with USB PDN/AN/A

The colorful logos are used primarily on packaging, not on devices themselves. The SuperSpeed logo means 5 Gbps, and the SuperSpeed+ logo with the "10" means that it's USB 3.1 Gen 2 (10 Gbps).

The tridents and the battery icons are to be used primarily on devices themselves. The trident with no letters indicates USB 2.0. The trident with "SS" means SuperSpeed, and the trident with "SS" and a "10" means SuperSpeed+. When you see the above trident symbols encased in a battery icon, it means that those ports support Power Delivery.

Note that other indicators point to a port's support of other protocols -- Alternate Modes (or "Alt Modes") -- such as the "DP" that indicates "DisplayPort." Note here that Alt Modes are part of the Type-C specification, not part of USB 3.1, and they require USB PD to operate.

These logos and stamps can be used together, too. For example, if you see that a given port is stamped with a little "SS" before it, followed by a 10, enclosed in a battery, with a DisplayPort logo next to it, you're looking at a port capable of 10 Gb/s of data throughput with USB Power Delivery, and DisplayPort as an alternate mode.

Why Are There Multiple Versions Of USB 3.1?

A critical thinker would, at this point, be wondering why anyone thought it was a good idea to have two different "USB 3.1" generations in the market at the same time. It seems ludicrous -- but in fact, that terminology was never meant to be marketing terms at all. "[The two versions of USB 3.1] were not originally intended for consumers, which is why we promote the use of the certified brands SuperSpeed USB and SuperSpeed USB 10 Gbps," said a USB-IF representative. "The terms 'USB 3.1 Gen 1' and 'USB 3.1 Gen 2' are revision nomenclature terms used to identify the proper revision level of a specification and were not developed to be consumer-facing."

Essentially, what happened is that those terms simply "gained traction in the marketplace," and thus the group was stuck having to explain the terms along with its "SuperSpeed" branding.

USB Type-C Does More Than USB 3.1

As we mentioned, "USB Type-C" doesn't mean "USB 3.1." Although many -- possibly, most -- applications of USB Type-C will involve USB (one "Gen" or the other), the USB Type-C port design allows for additional features.

For starters, there is USB Power Delivery, which is a feature that allows devices to deliver up to 100 W of power through a USB port. Not every USB Type-C port will necessarily have this capability (remember, USB PD is its own spec), but it is an essential part of creating a single-cable solution that offers both data transfer and charging.

This is a powerful feature (if you'll excuse the pun), because it means that you could, for example, connect your laptop or phone to your monitor using a Type-C port and cable, which would send audio and video to a monitor, and the monitor could simultaneously charge your laptop (as long as all connected devices support USB PD).  

Additionally, USB Type-C can support DisplayPort as an Alternate Mode, as well as MHL and Thunderbolt 3 (with Intel's new Alpine Ridge controller). Theoretically, one could route just about any protocol through USB Type-C. Again, this will only be supported if the controller behind the port supports it. (You'll be able to tell whether a USB Type-C port supports DisplayPort by whether it has a little DisplayPort logo next to it. See how the branding is helping already?)

Not All Cables (Or Ports) Will Be Created Equal

One USB Type-C cable won't be identical to another, which means consumers will have to be careful when buying one, paying close attention to a given cable's capabilities. Thunderbolt excluded, things are quite simple: Some cables will support USB Power Delivery, and others won't. Most cables will support no more than 65 W power delivery, while other, thicker cables can handle 100 W.  

Further, be aware that just because a Type-C port on a given device (or a specific Type-C cable) offers extra capabilities doesn't mean the device connected to it has the same. For example, if a cable has a male Type-A port at one end with four terminals, it will work no faster than a USB 2.0 cable (480 Mb/s), even if the other end is a USB Type-C plug.

One helpful factoid is that any USB 3.1-labeled cable will support both generations of USB 3.1. Therefore, whether the host has a data rate of 5 Gbps or 10 Gbps doesn't matter -- the cable will support it. (You'll only get the lowest common denominator performance, though, at 5 Gbps.) Again, however, a USB 3.1 cable doesn't necessarily support USB PD -- there will be additional markings for that.

When you take Thunderbolt into the equation, things will get a little more complicated, though. There will be three kinds of cables that work for Thunderbolt: up to 2 m-long passive cables that are limited to a maximum of 20 Gbps (Thunderbolt 2 speeds); 2 m-long active cables up to 40 Gb/s; and active optical cables, which can push 40 Gbps up to 60 meters.

Just One Problem…

All of the above is helpful information -- we've explained the key differences in current USB technologies and outlined how to identify them -- but there's one lingering issue: The branding is optional.

It is true that in order to use the branding, a given product must be certified by the USB-IF, which was a smart move on the group's part. The USB-IF trademarked the logos and branding, and OEMs can use them for free -- once they're certified. Therefore, when you see that branding, you can rest assured that it has passed the USB-IF's hundreds of tests. But because the branding is optional, the absence of the logos and stamps does not necessarily mean that a product has not passed certification.

OEMs can simply decide not to clutter up their sexy product designs with USB information. That's all well and good, but it creates a problem for consumers who then cannot tell, at a glance, what a given USB port can or can't do. Without the branding information, you have to go check the detailed specification list, and even then, OEMs may not have bothered to add clarification to those materials, either.

With USB 3.1 and USB Type-C, the USB-IF is stirring things up a bit. Rather than simply outing a new data rate and updating the Type-A, Type-B, Mini, and Micro connectors to enable the new data rate, there is more going on, and it will benefit the industry when features such as Alternate Modes and Power Delivery see wider adoption.

The next step is that OEMs need to help consumers by using the USB-IF's branding. And consumers should demand it.

Seth Colaner is the News Director at Tom's Hardware. Follow him on Twitter @SethColaner. Follow us @tomshardware, on Facebook and on Google+.