Original Thunderbolt Display to Thunderbolt 4 how exactly?

in disbelief wrote:

I was beginning to suspect Thunderbolt 3/4 was synonymous with USB-C, but had been told by someone who sold such products professionally that they were in fact different. Why Apple is so cryptic about the equivalence is baffling.

Thunderbolt 1 and 2 used the Mini DisplayPort connector - and were set up so that a computer (or chain of TB devices) could act like a Mini DisplayPort, for the benefit of a display or adapter at the end of the chain. While Wintel PC vendors had the option to build PCs with Thunderbolt 1 and 2 ports, few did.

When Intel was working on Thunderbolt 3, they saw the USB-C standard effort taking shape, and decided that Thunderbolt would have a brighter future on the USB-C connector. So they moved it there for Thunderbolt 3. Thunderbolt is just one of several protocols that USB-C ports can carry. Every Thunderbolt 3 or 4 port is – by definition – a USB-C port. But you can have USB-C ports that aren't Thunderbolt ports.

Some examples:

• The USB-C ports on 12" Retina MacBooks (Early 2015 – 2017). These USB-C ports support USB, DisplayPort, and USB-C Power Delivery, but not Thunderbolt.
• The front-panel USB-C ports on Mac Studios that have M1 Max and M2 Max processors. These support USB, but not DisplayPort or Thunderbolt.
• USB-C ports on most USB-C monitors with a resolution of 4K or less.
• USB-C ports on non-Thunderbolt hubs and docks.
• USB-C connectors for most USB-C flash drives and memory card readers.

Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter - Apple

(It works with Thunderbolt 3 or 4)

in disbelief wrote:

The only remaining question I have is: when I spoke to Apple about the issue I was told that I definitely want to use the HDMI port for video (I neglected to ask why). Is that accurate, and if so, is it a bandwidth/throughput consideration or something else?

As to the general question of when it is better to use a particular method, this depends on several factors, such as your computer's ports and capabilities; your monitor's ports and capabilities; and what adapters are available.

HDMI implementations have often lagged DisplayPort ones in their capabilities. Many years ago, I think that it was common for Macs to support 2560x1600 on Mini DisplayPorts or Thunderbolt 1/2 – but only 1920x1200 on HDMI.

A more recent example would be using HDMI with UHD 4K displays. Some displays can take 10 bits (instead of 8) for each color channel. This means that they can potentially divide whatever color space they support (a separate issue) into ~1 billion (2^30) gradations instead of into "merely" ~16.8 million (2^24) gradations.

If you take a look at the specifications for HDMI 2.0, you'll see that it imposes a tradeoff on such displays. See the chart in the "Specification Enhancements" section of https://www.extron.com/article/hdmi2faq . You can't have all of (4K resolution, 10-bits per channel, 4:4:4 coding (a fancy way of saying you actually get that resolution), and 50 or 60 Hz refresh rates). Something has to give. This is a tradeoff encoded in the HDMI standard and isn't a Mac-specific thing. So on a lot of Macs that have both USB-C (DisplayPort, Thunderbolt) and HDMI, if you want / need that last little bit of functionality that HDMI doesn't support, you'd want to use a USB-C or DisplayPort connection.

If you look at the current Mac minis,

• Those based on the base M2 chip have only two USB-C (Thunderbolt) ports, and they can drive a display at up to 4K resolution at 60 Hz over HDMI.
• Those based on the M2 Pro chip have four USB-C (Thunderbolt) ports, and they can drive a display at up to 8K resolution at 60 Hz over HDMI

I could be wrong, but I believe this means that the Mac minis based on the M2 Pro chip implement HDMI 2.1. The 2.1 standard allows for triple the bandwidth of the 2.0 one, so when you're working at the edges, that ".1" is more significant than it might first seem! And if you were using the HDMI port on a M2 Pro Mac mini to drive a monitor that had 4K resolution and a HDMI 2.1 (not 2.0) input port, the tradeoff described above would probably go away.

The more you're looking for "bleeding edge" resolution, 10-bit-per-channel color, > 60 Hz refresh rates, etc., the more you have to pull your hair out figuring out what all of the computer and monitor specifications mean … what standards allow … what the computer and monitor makers are oversimplifying and not telling you.

A lot of times, though, it will be "there are several ways which work; pick whichever is convenient."

in disbelief wrote:

The only remaining question I have is: when I spoke to Apple about the issue I was told that I definitely want to use the HDMI port for video (I neglected to ask why). Is that accurate, and if so, is it a bandwidth/throughput consideration or something else?

You would definitely not want to use the HDMI port to connect a 27" Apple Thunderbolt Display (or any other display that requires Thunderbolt input).

There are "adapters" that go from Thunderbolt (on the computer side) to HDMI (on the display side). We call them Thunderbolt docks or eGPUs. (Apple Silicon Macs don't support eGPUs; some Intel Macs did.). In these cases, the Thunderbolt signal from the computer is carrying encapsulated DisplayPort video, or acting like an external PCIe slot (just with less bandwidth than most PCIe slots). You're going from a more flexible interface down to a particular display-oriented one.

There are, to my knowledge, no adapters that go from HDMI (on a computer) to Thunderbolt (on an external display). If you were to plug in a USB-C (DisplayPort) to HDMI cable in reverse, thinking that the USB-C side would output a Thunderbolt signal to a monitor, you'd be disappointed. It wouldn't output Thunderbolt, and I doubt if it would even output USB-C-encapsulated DisplayPort to the monitor.

Whoever you spoke to was clueless.

If you look at > Connect a display to Mac mini - Apple Support

It clearly shows that you need to use a Thunderbolt 3 (USB-C) to Thunderbolt 2 adapter.

You're welcome.

Yea' don't be too hard on those front line support folks. They have a dot to dot troubleshooting script to follow and can not be expected to know everything about the inner workings of every device or setup.