I am confused about the Thunderbolt 4 bandwidth on the new MacBook Pro 14".
My understanding is that Thunderbolt 4 provides 40Gbps bandwidth. Is that across ALL the ports (shared), or does each port get it's own 40Gbps bandwidth?
40 Gbps is for display and data bandwidth combined. Thunderbolt 4 has similar capabilities to Thunderbolt 3 so I wouldn't expect more bandwidth.
Display data can be up to 34.56 Gbps for two displays (exception: Intel Macs with GPUs that don't support DSC may connect an XDR display using 38.9 Gbps). The M1 Macs support DSC, so each XDR is only 15.4 Gbps. An LG UltraFine 5K display is 29 Gbps (uses two DisplayPort connections so it counts as two displays). A 4K display is 16 Gbps.
Data bandwidth can use whatever remains of the 40 Gbps that is not being used for displays. However, there's never been a benchmark that has shown much more than 24 Gbps (3000 MB/s) from a single Thunderbolt device. I haven't seen a benchmark showing bandwidth for multiple Thunderbolt devices connected to the same port (in a chain or to a Thunderbolt 4 hub).
A Thunderbolt bus may have two ports and only support two displays (two to one port or one to each port). On Intel Macs with discrete Thunderbolt controllers the limit for data for both ports was ≈23 Gbps (using a RAID 0 between two NVMe or by using ATTO Disk Benchmark). For greater performance, you would need to connect the two devices to separate buses. Intel Macs with the Ice Lake CPU have integrated Thunderbolt (built into the CPU) so you could get ≈38 Gbps from any two or more ports (same or different buses). M1 Macs have integrated Thunderbolt also, so I would expect their behavior to be similar to the Intel Ice Lake option. I would like to see benchmarks for multiple NVMe connected to multiple ports and to a single port.
So, for example, if I dock the MacBook Pro 14" to a Thunderbolt 4 dock on one port (with devices connected to it), have a high speed SSD attached to another MacBook Pro port, and have an external display (display with USB ports that ALSO have devices connected) attached to the third Thunderbolt 4 MacBook Pro port, would they be cutting into each others bandwidth?
USB devices connected to a Thunderbolt 4 dock (including the audio, SD card, and Ethernet) share a 10 Gbps connection to the USB controller of the M1 Mac (USB tunnelling is used when both the host and the peripheral support Thunderbolt 4/USB4 - bypassing the USB controller of the dock - the bandwidth is similar whether USB tunnelling is used or not).
High speed SSD (up to 24 Gbps if it is Thunderbolt) connected to another port should get max performance if the M1 behaves like the Ice Lake (10 Gbps USB + 24 Gbps SSD is only 34 Gbps) or if it's connected to a separate bus.
A display connected to a third port shouldn't cause a problem with the other two ports since DisplayPort data on one port does not affect other data on other ports. A display may have a USB hub that uses 480 Mbps or 5 Gbps (I haven't seen any that support 10 Gbps). A display is usually less than 35 Gbps so there's enough bandwidth for 5 Gbps. Even if a display could use more than 35 Gbps, it would mostly only affect the write speed (display data is mostly host to device direction).
So the final tally is:
10 Gbps dock USB + 24 Gbps Thunderbolt SSD + 5 Gbps display USB = 39 Gbps. I think the M1 Mac should be able to handle this especially since it's unlikely for you to be using more than one device at the same time (you can certainly read and write simultaneously since read and write uses different lines).
One other question.... if the Thunderbolt 4 dock provides a max 90W charging power, would that still fast charge the MacBook Pro 14", or does it need a 96W charger still connected?
I am guessing that 90W can charge 93% as fast as 96W? Or I don't understand why the MBP wouldn't take full advantage of the 90W.
