I’m in the midst of preparing a review of the superb Nikon Z7 digital camera. I found one aspect of it seemingly disappointing. But it now seems almost certain that the problem wasn’t the camera, but the USB Type-C cable I was using. That cable was slow.

USB Type-C is different

Surely a cable is just a bundle of insulated wires connecting terminals in the plug at one end to terminals in the plug at the other. Right? Surely the only impact it can have on the speed of data transmission is the quality of the materials used to make it, and perhaps the length of the cable. Right?

Well, for most cables that is the case. It’s certainly the case for USB Type-A and USB Type-B and their micro and mini variants. All those are passive cables. They just carry the signal from one plug to the other.

But USB Type-C is different. It’s at least a partially active cable. It incorporates electronics – a chip – that identifies the capabilities of the cable.

What are those capabilities? Well amongst the capabilities of the USB Type-C connector identified by the chip are such things as:

. whether the cable supports USB Power Delivery and which modes (currently up to 60 watts).

. whether it supports so-called “alternate mode” operation. That means, whether it’ll work with DisplayPort, with Thunderbolt, with MHL or with HDMI.

. and whether it supports USB 2.0 data flow speeds (up to 480Mb/s), USB 3.0 SuperSpeed (up to 5Gb/s) or USB 3.1 SuperSpeed+ (10Gbps).

You can read GadgetGuy’s overview of USB cables and types here

Most are slow

So, here’s the problem: if you go into just about any store and purchase a USB Type-A to USB Type-C cable, it will be USB 2.0 rated. It’s not that it can go faster but may be limited by the quality of the cable. That has been the traditional limitation.

No, a USB 2.0 rated USB Type-C cable will tell the equipment it is connected to that it can only handle USB 2.0 speeds. USB 2.0 is specified at 480Mb/s, which converts to 60MB/s. For reasons I don’t understand, USB 2.0 rarely gets up near that full speed, and is very often less than half of that.

So even if the devices at both ends of the cable could support much higher speeds, and the quality of the cable manufacture itself would allow it to support much higher speeds, the data flow is still going to be throttled down to something under 60 MB/s.

Examples of slow and fast

Let’s look at some example cables. I had a few USB Type-A to USB Type-C cables around the office. I’d purchased some, while others had been given to me by vendors. For the most part I don’t even know the brands and I certainly no longer have their boxes. To test their speeds, I put a folder of files, mostly photos and video, on a LaCie 1TB Rugged USB-C external hard drive. The test folder amounted to 10.2GB and contained 1,183 files.

Then I just plugged the USB Type-A end of the various cables into a USB 3.0 port of my desktop computer, one by one, and the USB Type-C end into the drive. And I copied this folder onto the desktop from the LaCie to determine the speed.

LaCie says that the drive supports transfer speeds of up to 135MB/s. The difference between something nearing that and the much lower speed of a USB 2.0 cable should be apparent.