Thunderbolt 3 Bus versus Port ?

Question

Level 1

8 points

Thunderbolt 3 Bus versus Port ?

I'm a bit confused on bus versus port for TB3. My Mac Pro (2019) has 8 TB3/USB-C ports, 4 on the video card, 2 on the I/O card, and 2 at the top of the Mac Pro. But when I look at the Thunderbolt Device Tree, there are only 4 Thunderbolt Busses shown. My understanding is that I can daisy chain 6 devices together, but now I'm wondering if this is a per-bus limit, or a per-port limit. This is a theoretical question, as there are currently enough ports for me to spread devices around.

Mac Pro

Posted on Apr 18, 2020 3:12 PM

Reply

Answer 1

Top-ranking reply

BradSP

Level 1

75 points

Apr 18, 2020 3:27 PM in response to billie_a

The actual answer here is you will need to investigate exactly what you want to do rather than relying on the technical specs. I'd suggest the about mac is displaying what is currently connected so you would need to attach the other devices before they will show up. Next you do need to investigate those other devices and do not assume that you can daisy chain displayport monitors for instance. Apple does not support MST on the displays and you can find alot of information via google.

Reply

Answer 2

billie_a Author

Level 1

8 points

Apr 18, 2020 3:55 PM in response to BradSP

Thanks. I wasn't intending on daisy chaining displays. Currently, I have multiple storage devices that connect via TB3, plus some TB3 docks (whose primary purpose is to give me USB ports). I don't expect all the storage systems to be active simultaneously, so daisy-chaining them to share the 32Gbps data bandwidth seems okay (and I wouldn't put a 4k/5k display on the same chain anyways, since it would eat into that 32Gbps data bandwidth, if I understand this correctly).

Reply

Answer 3

billie_a Author

Level 1

8 points

Apr 18, 2020 4:02 PM in response to etresoft

That is a great diagram! Thanks! It answers my question completely, and makes clear all the caveats involved. For my intended purposes, the answer is each port can have 6 devices daisy chained, however the total TB3 bandwidth is shared between ports in the same TB3 bus. That is a key piece of information, so I'll be sure to keep that in mind when connecting devices to ensure devices are utilizing all the TB3 busses effectively.

Reply

Answer 4

etresoft

Level 9

50,854 points

Apr 18, 2020 3:50 PM in response to billie_a

It can be complicated. Here is a good diagram: https://www.owcdigital.com/assets/dealer/files/thunderbolt-daisy-chain-inforgraphic.pdf

Reply

Thunderbolt 3 Bus versus Port ?

Similar questions