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Technical analysis

Not all USB C ports are equal

I kind of already knew but not realized it, until I got my new Flex 15 from Lenovo. This laptop comes with one USB C port. Lenovo proposes a travel hub as an accessory. That hub fits into the USB C port, offering one USB 3.1 port, one HDMI output and one Ethernet port. Unfortunately, that hub won’t work, not because it is defective, but because it is not compatible with the Flex 15! This article tries to explain why and outlines some possible uses of the limited USB C port provided by that laptop.

USB C is the successor of USB 3.1, with a completely different connector. USB 3 connectors fit in USB 2 and even USB 1 ports, but USB C connector is not compatible with USB 3 ports.

The USB C connector looks as follows.

Example of a USB C connector

The port is also different, smaller than the USB 3 and the connector can be plugged both sides. The female connector looks like this.

USB C causes quite a bit of problems, because it is too new and because not all ports are equal, without any clear way of determining its capabilities. Main issues will be, for the time being, compatibility with existing devices and the different variants of host controllers.

New connector = new devices?

The first problem is compatibility. As the connector is different, a USB C port accepts only USB C connectors, but most USB devices at the time I’m writing this are USB 3, not USB C. This won’t be a problem on most systems. At worst, the USB C port will just be a cool artifact that will be never used, a bit like Firewire connector on some older laptops. However, there are some ultrabooks with just USB C ports, like Dell’s newer XPS models. I was quite shocked to see this and thought a user of such a machine would need to buy all new devices. That’s fortunately not the case, as I found out later.

Then, what can be done with that USB C port? First, a couple of devices have a USB C port and comes with a USB A to C cable. You can use that cable, or purchase a USB C to C cable to hook the device through the new USB C port. Examples of such devices are newer Android phones like the Google’s Pixel 2 and 3, V3 WASD CODE keyboards and the ROLI’s BLOCK and Seaboard.

I also found adapters turning a USB C port into a USB A; they look as follows.

A USB C to A adapter

Such adapters allow to use USB C ports like regular USB 3.1 ones, pretty much adding USB ports to the laptop.

Hubs also exist, but that’s were things become tricky and quite annoying. Some USB C ports are not compatible with all hubs!

Variants of host controller

The capabilities of the USB C ports depend not on the physical connector but rather on what is linking it to the system’s motherboard. We call this the host controller. As far as I know, there are the three following variants of such controllers.

  • Thunderbolt 3. This is the most powerful and versatile port. A Thunderbolt 3 port can be used as a regular USB 3.1 port using an adapter, it can carry over display information and can transfer enough power to charge most laptops. You’ll need a hub or docking station to expose this; the connector itself won’t allow it. Thunderbolt 3 also allows the transmission of PCI Express lanes through a cable, pretty much offering extensibility to a system. You can for example hook up an external graphic card or high performance hard drive. The problem with Thunderbolt is that the previous standard relied on a different mini-DisplayPort cable, and many devices will be claimed as Thunderbolt-compatible; you won’t know for sure it is Thunderbolt 2 or 3 unless you look very carefully on the device’s pictures, search on forums, email the vendor, and maybe even then, you may get a Thunderbolt 2 device while expecting a Thunderbolt 3 and have to return/exchange it. Quite annoying. A device claimed to be Thunderbolt 3 compatible should be fine though.
  • USB C with display and power. The port can be used for regular USB 3.1 devices (with an adapter or hub) or transfer display and power, enough power to charge a laptop through just that small USB C connector. Hubs providing HDMI output can be used with such ports. Some docking stations exist and can be used to charge a laptop and extend its display capabilities with one or two extra ports. Docking relying on proprietary connectors is now achievable with a generic, smaller, reversible connector. That’s quite amazing, and a USB C docking station should work with all laptops supporting USB C with display and charging, PC or Mac!
  • Regular USB 3.1 only. USB C doesn’t require support for display and power (Thunderbolt 3 does), so some vendors ship limited USB C ports that can just be used with adapters or hubs providing only USB C or 3.1 ports! Trying to hook up a hub or docking station with display or charging capabilities on such ports will likely fail. Windows will report the device malfunctioned, making you think it is defective. But it is not; this is the port that is limited. But not defective, it will work with USB 3.1 devices (with proper adapter).

Lenovo’s Flex 15 has such a limited USB C port. Hooking up the travel hub, offered as an optional accessory while purchasing the laptop, will always fail. The hub wasn’t defective, I tested it on my work’s laptop that has a USB C port with display support, and it worked. But not on the Flex 15. All that can be done with the hub is a RMA. Sad but true.