The M1 Macs were the first Macs with support for the Thunderbolt hub feature found in Thunderbolt 4. The move from Thunderbolt 3 to Thunderbolt 4 Isn’t this going to be a problem? It turns out that Thunderbolt 4 saves us here. I may have the same bandwidth from two Thunderbolt ports on the M1 Macs as I have on the Intel Macs, but I still can only connect two devices directly to this new Mac. What about only being able to connect two Thunderbolt devices to the M1 Macs? The results using AJA System Test show that the 2 Thunderbolt ports of the M1 Mac are indeed on separate Thunderbolt buses as I get over 3,500 MB/sec reading from my stripe volume. The total throughput of both ports together on a single bus is limited to 2,800 MB/sec. Since the two ports in a pair are connected to one bus, they share the Thunderbolt bandwidth. Each pair of Thunderbolt ports on my Intel Mac is connected to a single bus powered by a dedicated controller chip.

My other concern is that both my Macs only really have two Thunderbolt buses. On Intel Macs, each pair of Thunderbolt ports is actually one bus

Both of them have only one Thunderbolt connection, so they must either be connected to a dedicated Thunderbolt port on my Mac or be at the end of a chain of devices. My desire for more than two ports comes from using bus-powered devices like the OWC Envoy Pro EX and the OWC Thunderbolt 3 10G Ethernet Adapter. Both my 2019 16 inch MacBook Pro and my 2018 Mac mini have four Thunderbolt ports, and I can’t imagine using a Mac with only two. Having only two ports doesn’t seem like enough for professional use. I have read a lot of complaints about the new M1 based Macs only having two Thunderbolt ports.

Mac mini video cable