Although the SCSI parallel bus is pretty much dead and gone, the SCSI protocols are quite alive and well. They are used for the SAS (Serial-attached SCSI) interface commonly used in enterprise servers and it is also part of the USB 3 standard (UASP - USB-attached SCSI protocol).
Although Apple only supported 8-bit SCSI and “Fast” SCSI-2 interfaces (topping out at 5 and 10 MB/s (40 and 10 Mbit/s), respectively), there were many higher-capacity versions of parallel SCSI that Apple never used. The fastest being “Ultra-640”, which can deliver up to 640 MB/s (5 Gbit/s) using a 16-bit (68- or 80-pin) cable.
Of course, the most recent USB and Thunderbolt protocols are many times faster than this, but note that Ultra-640 was standardized in 2003. The SCSI people abandoned the parallel bus in favor of SAS, which began life as SCSI over physical SATA interfaces. SAS 4.0 (2019) goes up to 22.5 Gbit/s, comparable to modern USB interfaces.
SAS solves many of parallel-SCSI’s issues, including:
Point-to-point interfaces, so no device contention (unless a port expander is used)
No termination issues
No clock-skew issues
Up to 64K devices on the bus via port expanders (which can create a tree-like topology, similar to what USB and Thunderbolt 3 can do).
WhatCable only labels ports on the Mac Mini M4 Pro as Port-USB-C@1, etc. It skips C@4 and then shows C@5 and C@6 with nothing connected. Based on what it shows is connected to the cable, Why does it not list a Port-USC-C@4?
For the 2 ports with nothing connected, it tells me to plug a cable into the port to see what it can do. It must mean plug a cable into the port with a device connected. That makes sense as with no device connected, there’s no activity on the cable to measure. Is that a correct assumption?
It shows my TPLink 7-port USB hub and the drives connected, but does not show the cables from the hub to the drives or the empty ports. Is that normal?
I have a Dell 4K monitor connected to one of the Mac Mini USB-C ports and a Samsung 5K monitor connected to another. The monitors show up but the USB-A/C ports on each do not.
WhatCable only reports on cables directly connected to the computer, not on cables connected to ports on connected hubs. For example, it reports on the status of all ports connected to my Mac Studio, but not on the ports on my connected studio monitor.
Also, to get a complete report, you should have a device connected and running. For example, one of the Thunderbolt ports is connected to a Dell Monitor that is usually turned off. In that status, the cable is reported as a USB2 slow-speed cable. But when the monitor is turned on, it is reported as a data port cable running at full speed.
I assume (I haven’t use the app), that the three rear ports are 1, 2 and 3, and the front two ports are 5 and 6.
I suspect #4 is an internal device used for on-board peripherals. Apple no longer publishes block diagrams for their devices, but I remember plenty of diagrams for older Macs where internal devices (e.g., the Bluetooth adapter) are connected via an internal USB port.
So when the software enumerates all the interfaces, it gets these numbers from macOS, and the OS skips over those interfaces that don’t correspond to a physical USB port.
Are these Thunderbolt 3/4 or USB-4 monitors? If they configure the port into a Thunderbolt alternate mode, then they are not USB ports.
If so, then the ports on the monitor would be Thunderbolt devices and would appear as such to the Mac, and therefore to WhatCable.
Thanks, David. Your ID of the Mac Mini ports lines up with what I assumed,
The Samsung is connected to the Mac Mini via an Apple TB 5 cable.
The Dell is connected to the Mac Mini via an Hotron USB 3.2 Gen 2 cable. It’s thick like a TB4 cable, but I can’t easily get to the connector to check.
I just plugged an external drive into one of the Dell’s USB-C ports and then one of the USB-A ports and it shows up in both WhatCable and in the Finder.