Does each Thunderbolt 4 (TB4) port have its own independent bandwidth? Is the bandwidth limited for Data?

Do the four (4) TB4 ports on my 2023 Mac mini M2 Pro share the same "total" 40Gb/s bandwidth with each other?


If each TB4 port does have its own 40Gb/s of bandwidth, would each individual TB4 port have some of its bandwidth "reserved" for DisplayPort thus limited the amount of bandwidth for Data on that TB4 port?


The following are some of the comments I have read.


TB3 is limited to 22 Gb/s, because of the overhead for DisplayPort (whether DisplayPort is being used or not).

Note: I could not have a specific example for TB4.


The amount of Data that can be transferred, over TB3 / TB4, is adjusted "on-the-fly", depending on its use.

Note: This sounds to me like the bandwidth for Data would not be limited, if DisplayPort is not being used.


The Minimum bandwidth available for Data transfer is:

(TB4) 32Gb/s (or 4000MB/s)

(TB3) 16Gb/s (or 2000MB/s)


Thank you, in advance, for your time and assistance.


Mac mini, macOS 13.6

Posted on Nov 13, 2023 5:03 PM

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Question marked as Top-ranking reply

Posted on Nov 14, 2023 12:56 PM

Best info I found on it, by joevt...


Total bandwidth of M2 Mac mini with two Thunderbolt 4 ports: 80Gbps

Total bandwidth of M2 Pro Mac mini with four Thunderbolt 4 ports: 160Gbps

More like 44 Gbps for M2 and 88 Gbps for M2 Pro since data is limited to ≈22 Gbps per port (or maybe 24 or 25 Gbps in some cases).


The rest of the bandwidth of a Thunderbolt port can only be used for displays. The M2 and M2 Pro can only connect two displays to Thunderbolt. Display bandwidth is pixel clock x bits per pixel. bits per pixel is usually 30 but can be reduced to 12 for displays that support DSC.

4K60 = 16 Gbps

5K60 = 29 Gbps (LG UltraFine 5K - no other display can be connected to the same Thunderbolt port)

5K60 = 11 Gbps (Apple Studio Display)

6K60 = 15.4 Gbps (Apple Pro Display XDR)


Display bandwidth is mostly one way so it might reduce write performance if it exceeds 18 Gbps but have little effect on read performance.


https://forums.macrumors.com/threads/thunderbolt-4-ports-on-the-m2-mini.2377383/?post=31889428#post-31889428

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3 replies
Question marked as Top-ranking reply

Nov 14, 2023 12:56 PM in response to FrankPerry

Best info I found on it, by joevt...


Total bandwidth of M2 Mac mini with two Thunderbolt 4 ports: 80Gbps

Total bandwidth of M2 Pro Mac mini with four Thunderbolt 4 ports: 160Gbps

More like 44 Gbps for M2 and 88 Gbps for M2 Pro since data is limited to ≈22 Gbps per port (or maybe 24 or 25 Gbps in some cases).


The rest of the bandwidth of a Thunderbolt port can only be used for displays. The M2 and M2 Pro can only connect two displays to Thunderbolt. Display bandwidth is pixel clock x bits per pixel. bits per pixel is usually 30 but can be reduced to 12 for displays that support DSC.

4K60 = 16 Gbps

5K60 = 29 Gbps (LG UltraFine 5K - no other display can be connected to the same Thunderbolt port)

5K60 = 11 Gbps (Apple Studio Display)

6K60 = 15.4 Gbps (Apple Pro Display XDR)


Display bandwidth is mostly one way so it might reduce write performance if it exceeds 18 Gbps but have little effect on read performance.


https://forums.macrumors.com/threads/thunderbolt-4-ports-on-the-m2-mini.2377383/?post=31889428#post-31889428

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Does each Thunderbolt 4 (TB4) port have its own independent bandwidth? Is the bandwidth limited for Data?

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