About Macbook Air M1 USB-C port specifications. Two ports support for thunderbolt 3 or USB4. How about one port?

Both of the ports have the same specifications.

The ports are identical. You can use Thunderbolt 3 on either or both ports; you can use USB 4 one either or both ports. Either port will support any of the following:

Also see the following from MacBook Air with M1 chip - Tech Specs - Apple

Two Thunderbolt / USB 4 ports with support for:

• Charging
• DisplayPort
• Thunderbolt 3 (up to 40Gb/s)
• USB 4 (up to 40Gb/s)
• USB 3.1 Gen 2 (up to 10Gb/s)

USB-C is a "Swiss Army knife" type of connector. Some USB-C ports have a lot of features. Some don't.

The USB-C ports on a M1 MacBook Air are USB4 ports. That is, they support version 4 of the USB specification, whose name the USB Implementer's Forum has chosen to write without a space. The

• Charging
• DisplayPort
• Thunderbolt 3 (up to 40Gb/s)
• USB4 (up to 40Gb/s)
• USB 3.1 Gen 2 (up to 10Gb/s)

are different modes of operation that the computer, and the accessories attached to it, can select, as needed. If you attach most monitors, they're not going to know about Thunderbolt 3, and they're going to ignore it. They'll negotiate (or the adapter will negotiate) a USB-C (DisplayPort) connection.

If you attach an external USB hard drive or SSD, it might negotiate a USB-C (USB 3.1 Gen 2) connection.

TommyTommyChop wrote:

Thank you for your response.

The below comment is easy to understand for me that what USB-C is.

”USB-C is a “Swiss Army knife” type of connector”

I could understand that the port of M1 Macbook air is a USB4 so the port is compatibility to thunderbolt 3.

Thunderbolt is an optional enhancement to a USB-C port. My understanding is that it is an extremely common enhancement on Macs. I can think of only a couple of cases where Macs don't have it:

• 12" Retina MacBooks have USB-C ports that support (USB, DisplayPort, charging), but not Thunderbolt.
• The front-panel USB-C ports on Mac Studios with the M1 Max and M2 Max chips support USB – but not DisplayPort or Thunderbolt. For those, you use the full-featured USB-C ports on the back.

For USB4 host ports, my understanding is that

• Thunderbolt is optional. (Macs support it.)
• A new USB4 "up to 40 Gbps" USB transfer mode is optional. (Macs support it. No accessories do – yet.)
• USB 3.2 Gen 2x2 ("up to 20 Gbps") is optional. (Macs don't support it, and will fall back to "up to 10 Gbps" mode if you plug in an external USB 3.2 Gen 2x2 SSD.)

https://en.wikipedia.org/wiki/USB4

Note that the M1 and M2 MacBook Airs have a limit of one external display.

You can connect that display to either of the USB-C ports, using USB-C (DisplayPort) or Thunderbolt 3 (whichever is appropriate). You can't connect two displays at one time.

TommyTommyChop wrote:

I use one external monitor.

For me, I use my ipad for external monitor using sidecar.

This is three monitor system, macbook air display, external display and ipad display.

The "one external display" limit is for first-class, hardware-supported displays. There's hardware on the M1 chip whose job is to continuously refresh the internal display, and the one external display, without missing a beat and without putting much of the work on the main CPU.

Sidecar/iPad and AirPlay are more software-driven. The CPU has to take a more active role in packaging up video information and sending it over to the display device. So you might notice some "lags" that you don't see with the dedicated hardware monitor.

On the other hand, the Sidecar/iPad display doesn't count against the "one external display" limit. I do not believe that AirPlay does either. So you could potentially add another display by using AirPlay to an Apple TV set top box, or using AirPlay to another Mac that is recent enough to act as an AirPlay receiver.