Good question.
- Some Thunderbolt devices (mainly docks, but can be other device types as well) can connect via either Thunderbolt or USB 3.x.
Confused? Let's look into this a little more...
- We are familiar with the USB-C physical port. This port supports:
- Thunderbolt protocol
- USB 3.x protocol
- USB 2.x/1.x protocol
- DisplayPort protocol
- But not all USB-C ports support all of these protocols.
- If the USB-C port has a lightning logo next to it, then of course it supports Thunderbolt
- Thunderbolt, by definition, also supports DisplayPort
- So a lightning logo means that the USB-C port supports all 4 of the protocols above
- A USB-C port withouta lightning logo can support:
- USB 3.x
- USB 2.x/1.x
- DisplayPort (but only if the manufacturer chooses to support DisplayPort)
With that out of the way...
- We normally think that a Thunderbolt device connected to a USB-C port will only work if the USB-C port has a lightning logo next to it. And we would normally be right.
- But with Titan Ridge, Intel provided a new feature that allows a manufacturer to let their Thunderbolt device connect to a USB-C port that does not have a lightning logo.
- In other words, the Thunderbolt device can masquerade as a normal USB 3.x device and connect to the USB 3.x protocol on a standard USB-C port.
- This is called USB-C Alt Mode.
My Belkin Thunderbolt 3 Dock Pro, for example, is a Thunderbolt device that supports USB-C Alt Mode. When I connect it to a USB-C port with a lightning logo, it connects over Thunderbolt and operates at the full blistering speed of 40 Gbps (theoretical max).
But when I connect that dock to a standard USB-C port (without lightning logo) it still connects and works, but does so over USB 3.x and operates at whatever max speed that port allows (either 5Gbps, 10Gbps, or 20Gbps for USB 3.2 Gen 2x2). These are much slower speeds, but at least the dock works.