USB C - Whats the Go?


Continuing the discussion from Lightning cables recommendations?:

I don’t understand USB C nearly as well as I’d like to. I understand that USB C often refers only to the connector type and not about any of the capabilities of the cable itself. I understand this has led to much confusion and pain.

The simple (albeit more expensive answer) is to only buy thunderbolt cables so you never have an issue but I grant that that isn’t really the best answer. Even if you just make sure you’re buying USB 3.1 Cables chances are that would be enough for most people since they probably aren’t using thunderbolt anyway. I understand that full thunderbolt speeds get limited by length, 0.5M to get 40Mbit and 1.0M to get 20Mbit (Which I assume this has to do with signal loss and or latency over length), which also means they should be easy to spot… they are the short ones :stuck_out_tongue:

Another solution would be to colour code your cables making it easy to identify the one you might need. Again the concept being that you should stick to buying only USB 3.1 USB C cables to limit the pain.

So there are some details here and there are plenty of other articles out there too, although that’s where I’m struggling.

There are a plenty of articles that talk about the differences between connector shapes and sizes and speeds of different specs, but detailed information specifically about USB C and the issues above are harder to track down.

Bottom line here, USB C is a 24 pin connector that can do lots of different things, but the questions, all specifically about USB C cables.

What physical difference is there is a 2.0/3.0/3.1 rated cable?
Are makers simply not using all the pins?
Do they have all the wires but need to be a higher quality wire and/or have better shielding?

The same question is there about USB A too. USB 2.0 vs 3.0 is easy, there is extra pins. What is the physical difference between a 3.0 and 3.1 rated cable?

For example. I have an external enclosure for a SATA drive that is labelled as USB 3.1. It cable with a USB-A to Micro-B cable (with its tell-tale aqua USB A connector). I swapped that out for a USB-C to Micro-B cable which was labelled as USB 3.0. It’s plugged into the thunderbolt / USB C 3.1 point on my wifes iMac…. But what speed is that running at 3.0 Speeds or 3.1 Speeds?

Bottom line, what sort of devices does the average person actually have and what sort of cables to they really need? Sure high speed thunderbolt for external GPU, displays and possibly storage, but otherwise?? Wouldn’t these sort of devices likely have their cables all but permanently connected and sitting on a desk somewhere?
Sure, portable devices are always going to have their cables mixed up and lost, but does the average person really need more than a box of 3.0/3.1 specced cables?

Moar links:

So like I said, plenty of pages talking about the different speeds of the connections, none seem to be talking about what physically makes them different.


USB-C appears to be a bag of hurt


USB-C is a physical connector, that can carry 5 different modes: Power (up to 100w), USB data, USB Display Port Alternate Mode, Thunderbolt data (ie PCIe!) & Thunderbolt Display Port Alternate Mode.

So controller chips for USB-C can offer DisplayPort as an alternate mode. This is just like how Thunderbolt 1/2 in the past shared a port with Mini Display Port. In that case the data was added to the video port that already existed, but in the case of USB-C it was the other way around.

Of course then Thunderbolt 3 adopted the USB-C port too. So that port is shared between the USB and Thunderbolt controller.

Thunderbolt 3 controllers continue to also offer a display port alternate mode (just as it did in v1/2!). Importantly this is different (and better see below) from the USB-C Display Port.

So there are 4 possible modes for a USB-C port on a computer with a Thunderbolt chip and 2 on a computer with just USB-C (ie 12-inch MacBook). Both also offer pass through of the display port alternate mode.

In my experience, USB-C Display Port alternate mode is VERY unreliable. Most of the dongles and hubs are crap. On every Mac I’ve supported, the only reliable USB-C dongle is Apple’s HDMI one.

Also in my experience, Thunderbolt 3 Display Port alternate mode is rock solid. I generally use the OWC docks. It’s unsurprising really - USB controllers have always been CPU dependant and are usually crap. It’s a “cheap” protocol. Real external connectivity for pro devices has always been SCSI/FireWire/Thunderbolt. :man_shrugging:

So, that’s the ports and protocols.

The cables? A similar mess but they match the protocols basically. Apple’s included power cable is a cheap 2m USB v2 protocol cable that does power and USB 2 data only. I think the length may limit what the cable can do - I’m not an expert there.

For data just think of USB-C as an available USB cable-end like the A & B ports are. You can get cables with almost any connector on each end. What speed you get us usually determined by the non USB-C end. ie I have a USB-C to USB-B v2 cable to connect to old USB printers directly that obviously only gets 480mbs.

The Thunderbolt cables can be passive and full speed (40gbs) if under 0.5m, otherwise they need a controller. That’s why most devices (even the Blackmagic eGPU!) ship with a short cable. I have a 2m Belkin cable that supports 40gbs that was like $80 (that includes controller chips I think).

Ok. That was an epic post from my iPhone. :joy::thinking: