Mac Studio M2 Max Thunderbolt/USB Bus Management

You may find the following article helpful:

• Getting best performance from Thunderbolt on Apple silicon Macs: a practical guide - The Eclectic Light Company

A good rule of thumb is to connect your highest speed devices (displays and multi-drive enclosures) to every-other physical ThunderBolt port.

NB>> on the base Model Mac studio, the front USB-C port are specified to be limited to USB 3.1 speeds of 10 G bits/sec. The Max model has all ThunderBolt ports.

For estimating purposes, divide bits/sec by 10 to get Bytes/sec including overhead.

As I expected, my M2 Pro Mac mini has four Thunderbolt/USB4 Buses, with a corresponding USB-C-type port for each bus. Currently, each port has a maximum bandwidth of 40 Gbps; actual data throughput will vary depending on the device attached to it.

In my case, I have an OWC miniStack STX attached to Bus 2/Port 3, which is Thunderbolt 4 capable. It is getting the full 40 Gbps bandwidth. The miniStack also comes with three Thunderbolt 4 ports for addition devices, but I currently do not have anything connected to any of them.

Connected to Bus 3/Port 4, is a much older WD My Book Pro. It only supports Thunderbolt 2, with a maximum bandwidth of 20 Gbps. It also comes with an additional Thunderbolt 2 port for expansion. I also do not have anything attached to that port.

On the USB side, the mini sports six USB buses; five USB 3.1 buses & a single USB 3.0 bus. Maximum bandwidth is 10 Gbps for the 3.1 and 480 Mbps for the 3.0.

OK, so based on the Information in the article Tesserax so kindly posted,

"every-other port" is correct for Intel Macs, which use a two-ThunderBolt-port Intel chip for each Thunderbolt Bus.

Apple Silicon Mac use one Apple chip per Thunderbolt bus. This means heavily loaded performance will be much more even across all the ports. That is MUCH nicer than I expected.

I am pleased to say, I stand corrected.

Using (System Report):

On my M1 MacBook Pro 16-in.

When I look at My Thunderbolt Busses, I see there are three, each with nothing connected.

When I look at my USB Busses, I see three ports, each controlled by an AppleT6000USBXHCI controller.

The Belkin USB Gigabit Ethernet interface is connected to one USB port, and the speed on that Bus is reduced to the minimum needed to run that device, 5 G bits/sec.

On another USB Bus, I see my simple USB Hub for slow devices and charging, and its speed is reduced to only what it needs, 480 M bits/sec.

All that seems fine, Except:

Why does it seem like there are twice as many ports on the machine? It's as if each USB-C port has a "ghost" Thunderbolt port as well, which shows up, but 'nothing connected'.

¿Is just an artifact of the way System Report works? or is there more to this story?

Normally, I would expect so.

It is possible, given their limitation to at most 10 G bits/sec speeds that ALL are controlled by a single custom controller chip, or possibly by hardware inside the 'System-on-a-Chip'.

Fastest devices should be on Thunderbolt busses anyway, because ThunderBolt has twice the data pathways as USB.

If that is not adequate, you are welcome to disassemble yours when it arrives. I am confident you will find that each of every TWO adjacent thunderbolt ports is supported by a Thunderbolt controller chip.

Sorry, I don't have a definitive answer for you at this moment. When I get a chance, I'll do the same with my M2 Pro Mac mini (which comes with four Thunderbolt 4 ports) to see what I come up with in the System Report.

If I had to venture a guess, at this point, it would be that even if Apple Silicon can handle one Thunderbolt port per bus, they may have implemented it differently on each of their Silicon models.

Grant Bennet-Alder wrote:

NB>> on the base Model Mac studio, the front USB-C port are specified to be limited to USB 3.1 speeds of 10 G bits/sec. The Max model has all ThunderBolt ports.

I think you meant "The Ultra model has all Thunderbolt ports."

The base model is the one with the Max chip, and just "plain" USB-C ports (no DIsplayPort or Thunderbolt) on the front.

Servant of Cats--

Yes, you are right. I stand corrected.

The base model is a Max processor, the deluxe model is an Ultra model, and has three more Thunderbolt ports.

But, but, but... that supports the argument that Apple ThunderBolt interfaces (and likely their USB 'twins') are built into the 'system on a chip'. You get at most three on a Max chip, and to get the other three, you graft two Max chips into an Ultra.

that information is right here:

"every-other physical ThunderBolt port"