What is the USB-C upstream port used for on the Studio Display / Studio Computer ?

The USB-C Thunderbolt port is the port used to connect to the computer.

That USB-C Thunderbolt port…

• will receive video output (downstream) from the connected computer.
• can provide 96 watts power (upstream) to charge a Mac laptop.
• does not provide power (upstream) to a Mac mini or Mac Studio.
• provides a Thunderbolt-to-USB-C hub for the three (downstream) USB-C ports.

The Thunderbolt 3 (USB-C) upstream port is the one that you must connect to the Mac in order to use the display at all. The Thunderbolt connection can simultaneously

• Carry video from the computer to the monitor
• Carry USB data traffic between the computer and the downstream USB-C ports on the monitor
• Carry charging power (up to 96 W) to a Mac notebook

The single Thunderbolt port is the one that you use to connect the Studio Display to the Mac Studio.

The three USB-C port are used for connecting external USB drives and charging your accessories.

also see > https://cdsassets.apple.com/live/6GJYWVAV/start/ma2063_studio-display-qsg.pdf

mr_hi wrote:

Are ALL 4 of these ports on the back of the Studio computer all UPSTREAM?

All 4 of the ports on back of the Studio computer, or all four of the ports on the back of the Studio Display? Either way, with regards to a connection to a single display, the answer is No.

Assuming that you have a 27" Apple 5K Studio Display properly connected to one of the rear-panel Thunderbolt ports on a Mac Studio computer,

• The computer is upstream of the display, both in the sense of being the video source, and in a USB hub sense.
• Despite this, the ports on the computer are not normally called "upstream" or "downstream" ports. (Only one of those ports has any relation to the display, and that port is certainly not "downstream" of the display. While that port is "upstream" of the display, we wouldn't normally call it an "upstream port".)

MrHoffman has explained the designation of the ports on the 27" Apple 5K Display.

mr_hi wrote:

Are ALL 4 of these ports on the back of the Studio computer all UPSTREAM?

No.

From earlier in the thread:

The Thunderbolt port connects to the host, while the other USB-C ports connect to other devices.

Those other devices are then accessible to the host.

In a manner of consideration, this display acts as a powered USB hub.

What does upstream mean in IT?

In IT operations, upstream refers to the direction of network traffic as it relates to device communication and dependency. Equipment that gives commands to other devices is considered to be upstream from those devices. For example, an application server is upstream of its dependent applications.

Upstream vs. Downstream

Even if there is bi-directional communication between devices, upstream and downstream, the upstream component is regarded as dominant and the downstream device is dependent.

https://sciencelogic.com/glossary/upstream#:~:text=In%20IT%20operations%2C%20upstream%20refers,upstream%20of%20its%20dependent%20applications.

The Studio Display's upstream Thunderbolt 3 port is the one that you connect to one of the Mac Studio's Thunderbolt ports.

see > https://cdsassets.apple.com/live/6GJYWVAV/start/ma2063_studio-display-qsg.pdf

That upstream Thunderbolt port on the rear of the Studio Display is what you would plug into a Thunderbolt port on the back of the computer. For example that upstream Thunderbolt port is connected to a Thunderbolt port back of my Mac Studio. The Studio Display comes with a Thunderbolt cable for connecting to a computer.

Below is the rear view of a Mac Studio computer:

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