The Importance of Choosing the Right USB Cable

Updated March 28, 2024

I already wrote about my trip to Spain and Europe and choosing the camera. Traveling with the Nikon Z7 II was definitely the right choice for me. What I haven’t mentioned was that I packed the wrong USB cable.

No, I’m not that stupid as to choose the wrong type of USB cable, say USB-C/USB-A instead of USB-C/USB-C. Still I made the wrong choice that would haunt me on my entire 6 weeks trip.

Cable ≠Cable

The MacBook Pro comes with USB-C connectors, same as the Sony MRW-G1 CFexpress type B reader. Besides USB cables that are sort of permanently connected to my workstation, I keep a bunch of spare USB cables in a drawer. So when packing, I chose the first USB-C to USB-C cable I could find.

First day in Madrid I took some 150 photos. Back at my hotel I started to transfer them to the computer. How long can a transfer from an external SSD drive to a NVME drive in the MacBook Pro take? With a file size of around 50-60MByte, the entire days shoot was a little over 9 GByte.

As I write this, I stopped the transfer time from an external Samsung SSD to my workstation (housed in an older chassis without front-side USB-C) using a USB-C to USB-A cable. The entire transfer finished in 20 seconds, that is 450MB/s.

Back in Madrid, it took nearly 10 minutes to transfer the same files from the memory card to the MacBook Pro! For sure it’s not the Sony CFexpress reader since at home it works really fast with the same USB-C to USB-A cable I used in the test above. My CFexpress cards are also very fast. So what is the reason that on my trip in Europe the file transfer speeds were so low, both from the CFexpress reader to the laptop and from the laptop to the external SSD drive?

Back home I tried a different USB-C to USB-C cable, a short ~35cm/1ft cable I found in my drawer. Whoa, what a difference! Around 250GB of photos were transferred within a few minutes. Can it be that a USB cable can make such a difference?

Test and Mark Your USB Cables

To avoid the wait, which literally cost me hours on my trip, you should test and mark your USB cables. This is the safest way to ensure you use the right cable. After closer examination of the cable I discovered that I had packed a cable that came with my Logitech wireless mouse.

Even modern USB-C cables come in different standards, including USB-2 which is slower than molasses. For file transfers you want at least USB-3, better USB-3.1, USB-3.2, USB-3.2 Gen 2, or USB-4. Yep, there are many standards, just to confuse you. A good overview of different cable types and standards, and what speed you can expect, can be found at this website (this is NOT an endorsement of the company!).

USB-A plugs usually have color markings – blue is good, red is better. Unfortunately USB-C to USB-C cables don’t have color markings, at least none of mine has. See the link above for more information.

Another way to ensure performance is by labeling the cables as you get them. My two short USB-C to USB-A and USB-C to USB-C cables came with the Sony CFexpress reader. They should support the speed of the reader. Don’t bet on that for cheap Chinese knockoffs or no-name products, though.

The cable I had taken on the trip was for powering and/or connecting a mouse, which runs perfectly fine at USB-2 speeds. A USB cable designed to meet USB-2 standard, that is up to 480Mbps, can never exceed that speed.

There are also substantial quality differences. Many cables are made to charge phones or mobile devices, but not for fast transfers. But even cables supplied with aftermarket USB chargers are often outright junk! Recently I threw away 3 out of 4 cables that came with aftermarket chargers since they couldn’t even charge a cell phone.

Measure the Transfer Speed

The best way to check your cables is by testing them. Connect your external device (SSD drive or memory card/reader) using the cable you want to test. Choose a folder with files of about 1o Gigabyte. Open your alarm/stop watch application on the cell phone. When ready, copy the folder to the external device and stop the time it takes.

This isn’t the most accurate way, but will give you a good idea of what to expect. Since data transfer speeds are measured in megabit per second and file sizes in megabytes, it might be helpful to get some correlation between the two. Here my translation of speeds:

  • USB 1.0: 12 Mbps ≈ 1.5 Megabyte/sec
  • USB 2.0: 480 Mbps ≈60 Megabyte/sec
  • USB 3.0: 5 Gbps ≈ 625 Megabyte/sec
  • USB 3.2 Gen 2: 10 Gbps ≈ 1.2 Gigabyte/sec
  • USB 3.2 Gen 2×2: 20 Gbps ≈ 2.4 Gigabyte/sec
  • USB 4 Gen 2×2: 20 Gbps ≈ 2.4 Gigabyte/sec
  • USB 4 Gen 2×3: 40 Gbps ≈ 4.8 Gigabyte/sec

Above transfer rates are the maximum possible speeds supported by the respective standard. In practice transfer rates will be lower. Other limiting factors are the kind of storage media or device that is connected on either end. Supposing you chose the right cable, the transfer speed will be determined by the slowest storage device.

Here is a list of storage device/media types and the approximate sequential read/write speed you can expect:

  • HDD SATA-3 (good old magnetic hard drive) ~ expect 80-160, the fastest reach 250 Megabyte/sec
  • 2 HDD in RAID-1 ~ around 160-300 Megabyte/sec read, write is same as HDD
  • SSD ~ 200-500 Megabyte/sec read, write usually lower
  • NVMe M.2 ~ 500-3800 Megabyte/sec read, write similar or lower

PetaPixel did some testing of CFexpress type B cards and a new USB-4 reader. It seems that USB-4 can break existing barriers.

Thom Hogan recently also posted on the subject of USB cables: Thank You EU and USB Standards Committee.


The USB-C standard is a mess, specifically cable identification. The market is flooded with junk cables that aren’t worth a cent.

When you buy peripherals like a CFexpress reader or external SSD that come with cables, test them and mark them.

If you’re in the market for a USB-C cable, buy from a respectable manufacturer and/or store. Have a look at that great video “A Look Inside Apple’s $130 USB-C Cable” on Adam Savage’s YouTube channel! Not only do they show CT scans of a quality Apple USB-C/Thunderbolt cable, they scanned some low-cost cables to compare. It’s literally an eye-opener on how some vendors cheat you. Did you ever sue a vendor for a <$10 cable that doesn’t work? Probably not, and that’s how millions of people end up spending money on useless junk.

Author: Heiko Sieger

The day has 24 hours. If that isn't enough, I also use the night.

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