USB-A is the original socket for USB at the PC end. There are 2 variants of it, the first is for USB 1.1 to USB 2 and the second is for USB 3 which adds extra pins in a plug and socket compatible manner – you can plug a USB-A device into a USB-A socket without worrying about the speeds of each end as long as you don’t need USB 3 speeds.

The differences between USB-A and USB-C are:

  1. USB-C has the same form factor as Thunderbolt and the Thunderbolt protocol can run over it if both ends support it.
  2. USB-C generally supports higher power modes for charging (like 130W for Dell laptops, monitors, and plugpacks) but there’s no technical reason why USB-A couldn’t do it. You can buy chargers that do 60W over USB-A which could power one of our laptops via a USB-A to USB-C cable. So high power USB-A is theoretically possible but generally you won’t see it.
  3. USB-C has “DisplayPort alternate mode” which means using some of the wires for DisplayPort.
  4. USB-C is more likely to support the highest speeds than USB-A sockets for “super speed” etc. This is not a difference in the standards just a choice made by manufacturers.

While USB-C tends to support higher power delivery modes in actual implementations for connecting to a PC the PC end seems to only support lower power modes regardless of port. I think it would be really good if workstations could connect to monitors via USB-C and provide power, DisplayPort, and keyboard, mouse, etc over the same connection. But unfortunately the PC and monitor ends don’t appear to support such things.

If you don’t need any of those benefits in the list above (IE you are using USB for almost anything we do other than connecting a laptop to a dock/monitor/charger) then USB-A will do the job just as well as USB-C. The choice of which type to use should be based on price and which ports are available, EG My laptop has 2*USB-C ports and 2*USB-A so given that one USB-C port is almost always used for the monitor or for charging I don’t really want to use USB-C for anything else to avoid running out of ports.

When buying USB devices you can’t always predict which systems you will need to connect them to. Currently there are a lot of systems without USB-C that are working well and have no need to be replaced. I haven’t yet seen a system where the majority of ports are USB-C but that will probably happen in the next few years. Maybe in 2027 there will be PCs on sale with only two USB-A sockets forcing people who don’t want to use a USB hub to save both of them for keyboard and mouse. Currently USB-C keyboards and mice are available on AliExpress but they are expensive and I haven’t seen them in Australian stores. Most computer users don’t wear out keyboards or mice so a lot of USB-A keyboard and mice will be in service for a long time. As an aside there are still many PCs with PS/2 keyboard and mouse ports in service so these things don’t go away for a long time.

There is one corner case where USB-C is convenient which is when you want to connect a mass storage device for system recovery or emergency backup, want a high speed, and don’t want to spend time figuring out which of the ports are “super speed” (which can be difficult at the back of a PC with poor lighting). With USB-C you can expect a speed of at least 5Gbit/s and don’t have to worry about accidentally connecting to a USB 2 port as is the situation with USB-A.

For my own use the only times that I prefer USB-C over USB-A are for devices to connect to phones. Eventually I’ll get a laptop that only has USB-C ports and this will change, but even then adaptors are possible.

For someone who doesn’t know the details of how things works it’s not unreasonable to just buy the newest stuff and assume it’s better as it usually is. But hopefully blog posts like this can help people make more informed decisions.

8 comments to USB-A vs USB-C

  • Denvercoder9

    Your list of differences between USB-A and USB-C is not entirely correct.

    Regarding #2, the higher power modes require a negotiation to take place before they can be enabled. This is necessary because the higher power requires higher voltages, and devices have to indicate support for that. This negotiation takes place over the CC wires, which are not present in the USB-A connector. There’s some proprietary solutions misusing another wire for the negotiation, but nothing standardised.

    Regarding #4, the USB-C connector has 4 differential pairs (wire pairs) available for high-speed signalling, while the USB-A connector has only 2. These extra pairs are required for all speeds above 20Gbps (technically, the “x2” variants of USB3/4 Gen 1-3 and all variants of USB4 Gen 4).

  • Frank Gevaerts

    The one thing where USB-C is very much worse is clarity. With USB-A there’s “is it USB 2 or USB 3?” but usually USB 3 is blue so that’s easy (and technically it *could* be a pre 2.0 cable), with USB-C who knows? Does this cable just do USB, does it do PD, does it do display? The only way to find out is to try. It’s really not the best end user experience at all.

    Denvecoder9: The Wikipedia page says that USB-A and USB-B can be used for PD to provide more than the 7.5W provided by the BC standard.

    The adverts for power supplies with USB-A sockets commonly advertise them as being cable of 18W, I don’t know if that’s an official standard but it’s probably some less formal standard or a Qualcomm standard if it’s not official. I did a quick test of a Huawei Mate 10 Pro on such a socket and it was pulling just over 9W.

    You are correct that for the very highest speeds it’s only USB-C. But there aren’t a lot of devices that can do such speeds. 2.5Gbit Ethernet is new and not that common and all the cheaper NVMe devices can’t sustain 5Gbit speeds for writing. I have 2.5Gbit Ethernet running at full speed on USB-A and when copying data to/from NVMe devices the speed of the USB-A port hasn’t been the bottleneck yet. For laptop docks USB-C is definitely the only good option.

    Frank: Yes if you want an emergency recovery device then USB-C is good for that. If you have more time to set things up then you can look at the ports and see which one is best.

  • Denvercoder9

    etbe: Hmm, you seem to be right about USB-PD supporting USB-A, though it seems to be only PD 1.0, and I’ve never seen that in the wild. This StackOverflow answer supports it never being used in practice: Most (maybe even all) devices I’ve encountered require at least USB-PD 2.0, and based on that SO answer, USB-PD 1.0 didn’t support anything above 100W anyway.

    Yes, Frank is right, everything USB-C is opaque and messy.

  • > I haven’t yet seen a system where the majority of ports are USB-C but that will probably happen in the next few years.

    Framework laptops only have usb-C, (4 on my 14″ one, 6 on the big one), but they’re recessed into the body and you stick little “adapter” cards into them that give you USB A, USB C, display port, HDMI, ethernet or micro SD card reader (plus various homebrew projects),

  • Denvercoder9: I agree that USB-C is the only viable option for charging laptops and other high power uses, whether 100W is possible in the specs doesn’t matter much if almost no-one makes PSUs or cables that can do it. I didn’t write this post about USB charging but about connecting devices to computers. If you want a USB ethernet device or USB mass storage you don’t need much power.

    It would be nice to have a USB-C powered and connected SATA disk caddy. But given that my experience is of PC USB ports not being able to properly charge phones like the Librem5 I doubt that will be generally usable any time soon.

    John: Yes Framework makes some really nice gear. One issue I have is that it doesn’t have a TrackPoint, I’ve been paying extra for Thinkpads for 26 years and the Trackpoint is a large part of the reason for that. If I had to buy a new laptop then Framework would be more appealing, but comparing an almost new condition Thinkpad for under $400 with the price of a new Framework laptop the Thinkpad is very appealing. Framework does reduce environmental issues, but buying second hand gear also achieves that goal.

    If they made a Framework phone or tablet then I’d be more interested.

  • Given the modular construction of the Framework laptop a trackpoint might be possible, although the keyboard might not be deep enough. (Personally I detest trackpoints :)).

    As for the phone, I’ve been a fairphone user since the FP2.

  • John: Yes a trackpoint would certainly be possible and technically it shouldn’t be difficult, it just needs a certain minimum quantity of units sold to not be ridiculously expensive. The Framework is far from the most popular laptop and only a tiny portion of laptop users like the trackpoint as much as I do so it seems unlikely that it could be made at a good price.

    The Fairphone company is doing some really great things and their hardware is nice. But they are expensive to buy and hold their value well on the second hand market so I can’t just buy a couple of them for testing the way I did with Note9’s for Droidian.

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