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After I told two people I transfered data between two laptops using a LAN cable, they said they had just used an USB A to USB C cable to connect them (the ones to charge phones). I do know that is impossible for type A-A USB cables, (this can also be found here) because the laptops would both want to be master and would each send 5V over the BUS essentially grilling the USB ports (thats why I dont want to risk just trying it out). However I dont know about USB type C and would be quite happy if someone could verify their claim.

As this answer about USB C to USB C cables suggests, this is possible with smartphones, but there are currently no laptops with the same Dual Role functionalitly.

TheFibonacciEffect
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  • I just tried this with a type C chromebook tablet and a type A windows laptop and nothing happens except the laptop is charging the tablet. If I connect the type C of both it would actually charge the other direction by default.....However, if you make yourself a special cable with 2 2.5GbE adapters and a cat 6 cable in the middle, it will work exactly as you described. – user3528438 Jun 19 '20 at 05:54
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    So no data transfer was possible when connecting the chromebook to the laptop? The second option is exactly what I did, I used two USB-LAN adapters and a LAN cable. – TheFibonacciEffect Jun 19 '20 at 06:05
  • Nope. Totally doesn't work. – user3528438 Jun 19 '20 at 06:35
  • USB C is 'smart', USB A has 'master' & 'slave' plugs so you can't physically connect two 'masters'. – Tetsujin Jun 19 '20 at 07:38
  • So I can transfer files using a phone charger? – TheFibonacciEffect Jun 19 '20 at 07:41
  • Does this answer your question? [Is there some way to connect two computers using USB?](https://superuser.com/questions/863/is-there-some-way-to-connect-two-computers-using-usb) – Attie Jun 19 '20 at 10:45
  • " I do know that is impossible for type A-A USB cables " This is not impossible, A-to-A cables have been specified as valid for host to host communications in the USB 3.0 spec which was released in 2010. There's documentation on the Microsoft website on how to use them for kernel debugging. It's possible but not widely supported. Part of the USB 3.0 A-to-A cable spec is to leave the 5 VDC line unconnected to avoid the hazard you fear. – MacGuffin Oct 19 '21 at 23:33

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The other questions / answers that exist on this topic are typically outdated, and do not consider USB C.

While USB C does offer "Dual Role" mode (somewhat similar to USB OTG), which would theoretically make this possible, it must be supported by the hardware and operating system, not just the physical connector.

As far as I know, Windows does not support device-mode or Dual Role operation, even if your hardware does support it... but I have found this page suggesting otherwise: USB Dual Role Driver Stack Architecture.

Linux does support this and allows you to make use of "USB Gadgets" to present the Linux system to the other device as a mass storage device (MSC), Ethernet interface (CDC-ECM), among others...

As mentioned above however, it is unlikely that even a modern laptop would support this mode of operation (though I'm happy to be told otherwise!). This feature is more commonly found in the chipsets used for embedded devices and phones.

Attie
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  • Dual role ports are not required, host to host communications have been in the USB spec since USB 3.0 in 2010. Dual role ports would certainly be helpful but not required. To see if a laptop with USB-C supports dual role try plugging it into another computer with a C-to-A cable, it should try to charge (and may be successful in this) and if it shows as a billboard device in Device Manager or equivalent utility then it has dual role hardware. – MacGuffin Oct 19 '21 at 23:43
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It should be possible to connect two laptops by a USB-C to USB-A cable and transfer data. I have not seen this work except for Apple laptops in Target Disk Mode. This worked very well for me in the past to get software onto my brother's cantankerous laptop when we could not find a USB drive for the transfer. We had no USB drive but we did have a USB-C to USB-A cable. I downloaded the files off the web, booted my MacBook (with USB-C ports) into disk mode, plugged it into his (older with USB-A) MacBook, and copied the files off my drive to his.

The various parts Apple used in their Intel based laptops are not all that unique, it's pretty much all off the shelf stuff that nearly every other laptop maker uses. The USB controllers they use are common and this can be verified by comparing the PCI identifiers as shown in some hardware diagnostic utility.

If Apple supports data transfer from a laptop with USB-C to another laptop with USB-A by a common USB-C to USB-A cable then why don't other laptop makers? That's a good question that I have seen asked for many years, though not always in those words. The hardware is there, and has been common in laptops for years now. The USB 3.0 spec allowed for host to host communications by a USB-A to USB-A cable, and that was written in 2010. The USB-C spec came out in 2014, and Apple supported Target Disk Mode by USB-C in 2015. With host-to-host communications being part of the USB 3.x spec for a decade there's no need for a dual role USB-C port to transfer data, but with a dual role port it can mean the computer with the USB-C port can pretend to be a USB drive so the computer with the USB-A port needs no special software.

This is possible and it's been done. There's other examples besides a MacBook in disk mode to prove it possible. The question in my mind is why is this not a standard feature in every operating system today?

MacGuffin
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