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Does the M4 Pro Thunderbolt 5 implemenation support USB 3.2x2?

Thunderbolt 5 supports 20Gbps USB 3.2x2 tunneling, however, it's optional. Does anyone know if the M4 Pro's T5 implementation supports it? If no one does, I'll be testing it out on a Macbook tomorrow and I'll answer my own question.

Mac mini (M4)

Posted on Dec 2, 2024 12:58 PM

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16 replies

Dec 14, 2024 5:49 PM in response to jonljacobi

From what I've read, USB4 defines three different and incompatible "up to 20 Gbps" USB transfer modes.


Two of them are new, and at least one (which has the marketing name "USB4 20 Gbps") is mandatory for USB4 host ports. USB 3.2 Gen 2x2 is optional for USB4 host ports.


Can you say "thrown under the bus"?


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Thunderbolt 4 may introduce new wrinkles for devices connected via Thunderbolt 4 hubs and docks. I just came across this article, and was surprised to read that with current chipsets, Thunderbolt 4's hubbing ability comes at this non-obvious cost.


Other World Computing – Blog – What’s the Difference Between Thunderbolt 3 and Thunderbolt 4?

"Because of the difference in how Thunderbolt 4 allocates data, every port on a Thunderbolt 4 device that isn’t Thunderbolt must share a single 10GBps slice of USB bandwidth."


So theoretically, that might mean that

  • Apple could support USB 3.2 Gen 2x2 for USB devices and Thunderbolt 3 docks – but doesn't.
  • There is no way to support USB 3.2 Gen 2x2 speeds on current Thunderbolt 4 docks, even if the host is capable of supporting those USB speeds in other contexts.


As for Thunderbolt 5, I don't have enough information to say.

Dec 21, 2024 4:44 PM in response to Grant Bennet-Alder

Grant Bennet-Alder wrote:

<< Not sure what you mean by genuine [ThunderBolt devices]... >>

MANY users think their drive enclosures are ThunderBolt devices, because of Hype from the makers or sellers, when they are merely USB-C v3 devices.


Apple likes to call the USB-C ports on Macs Thunderbolt ports or USB4 / Thunderbolt ports whenever they can, to emphasize the higher-end features of these ports that aren't always present on any old USB-C port.


A lot of accessory vendors, especially on places like Amazon, throw around around terms such as Thunderbolt or Thunderbolt-compatible loosely when describing

  • Display adapters that go from USB-C (DisplayPort Alt Mode) to (whatever)
  • Docks and hubs that use (USB 3, DisplayPort Alt Mode, Power Delivery), but not Thunderbolt
  • etc.

This leads many customers to believe that they are using, or require, Thunderbolt devices, when the logic is really more along these lines:


  1. All Thunderbolt 3, 4, and 5 ports, by definition, have USB-C connectors.
  2. All Thunderbolt 3, 4, and 5 ports on Macs support USB 3, DisplayPort Alt Mode, and in the case of a notebook, USB-C Power Delivery from an external power supply to the notebook, as well.
  3. Thus if a Mac user has a Thunderbolt 3, 4, or 5 port, they can count on our USB-C accessory (which uses one or more of (USB 3, DP Alt Mode, PD to the Mac)) working on that Thunderbolt port, even though the accessory doesn't use or understand Thunderbolt.

Dec 14, 2024 10:30 AM in response to jonljacobi

Intel finally got back to me on this. Alas, the email wasn’t specific in its USB terminology (thinking perhaps that I knew all the USB specs by heart), but the way I read it this may be their doing. What they said is that any USB device connected to a Thunderbolt 5 port uses the straight USB protocol (apparently not including 3.2x2 which uses two extra data lanes). If however a dock is connected, it uses the USB4 spec tunneling and could feature a 3.2x2 port that uses the tunneling protocol.


So I’m thinking it may simply be impossible for Apple to implement support for 3.2x2 directly connected to a Thunderbolt 5 port. I suppose a vendor could include firmware on a drive that would tunnel, but I’m not sure how or how difficult that would be.


Having not heard from Apple after direct inquiry, I’m not going to bother apologizing to them. Please don’t take this as fact, this is my interpretation of an email that didn’t spell out everything in fine detail.


Dec 21, 2024 12:45 PM in response to Grant Bennet-Alder

Not sure what you mean by genuine, but it’s always been true that the adapter doesn’t pass power. I didn’t have a AC-driven Thunderbolt 2 dock with me to test, but that’s always been necessary if you want to run a bus-powered Thunderbolt 1/2 SSD post-adapter. I’ve never tried other devices like HDMI displays or USB peripherals post adapter, but I think if I can find one of these docks (I’ve hidden them somewhere as I’ve no need on my newer Mac Studio) I shall.


Also, I’m just happy my audio interface still works! I can grab an M4 Pro Mini and not have to upgrade!



Dec 21, 2024 3:15 PM in response to Grant Bennet-Alder

USB and Type-C/USB-C are indeed very confusing for some users and certain journalists and marketing folks have further muddied the waters. Thunderbolt using the same type of port and connector certainly doesn’t help. There’s nothing for that other than reading fine print and doing your homework.


When you said genuine, I extrapolated sideways to fake, i.e. falsely advertised. But I haven’t seen any vendors claim their Type-C USB products are Thunderbolt. Maybe there are, and I just haven’t seen them.


Further confusing the picture… There were third-party adapters that were unidirectional — allowing you to connect T2 devices to T3 Macs, but not allowing you to connect T3 devices to T2 Macs.


https://www.macworld.com/article/233893/how-to-use-any-thunderbolt-device-on-any-thunderbolt-macand-we-mean-any.html


Dec 21, 2024 5:00 PM in response to jonljacobi

jonljacobi wrote:

Further confusing the picture… There were third-party adapters that were unidirectional — allowing you to connect T2 devices to T3 Macs, but not allowing you to connect T3 devices to T2 Macs.

https://www.macworld.com/article/233893/how-to-use-any-thunderbolt-device-on-any-thunderbolt-macand-we-mean-any.html


The StarTech adapter is one of those.


It has the same limitation as the Apple Thunderbolt 3-to-2 adapter as far as not being able to present a "plain" DisplayPort signal on the Thunderbolt 2 side. It has the additional limitation of being unidirectional. You cannot use it to connect a powered Thunderbolt 3 dock to an older Thunderbolt 1/2-equipped Mac.


The price on the StarTech site ($35.99 USD) is much more reasonable than the prices which people are trying to get for it on Amazon ($55.55 – $167.67), all of which are higher than the price of the bidirectional Apple adapter!

Does the M4 Pro Thunderbolt 5 implemenation support USB 3.2x2?

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