Thunderbolt 2 to Thunderbolt 4 adaptor

dkcrystal wrote:

Thanks - I’m still confused because the article suggested below seems to say I need USB C adaptor for 2025 MB air - though Apple say TB4 and USB C are not the same.

It states, “This adapter is not compatible with USB-C ports that don't support Thunderbolt 3, such as USB-C hubs or the USB-C port on MacBook models from 2015 or later.”

Your new MacBook Air has a TB4 port, not a USB-C port that some MacBook Air models had 8-10 years ago. The TB4 port on your Mac also supports TB3. The Apple adapter is what you need.

dkcrystal wrote:

Is there a thunderbolt 2 to thunderbolt 4 adaptior so I use my Macbook Air 2025 with my thunderbolt display? I can only find thunderbolt 3 to thunderbolt 2 on the Apple web site. Will that do the job?

It will if this is a 27" Thunderbolt Display.  The Thunderbolt Display has

• A hydra cable with two heads:  Thunderbolt (Mini DisplayPort connector) and MagSafe
• FireWire and Ethernet hub ports

It won't if this is the very similar 27" LED Cinema Display.  The LED Cinema Display has

• A hydra cable with three heads:  Mini DisplayPort, USB, and MagSafe
• No FireWire or Ethernet hub ports

For that display, you need a third-party USB-C (male) to Mini DisplayPort (female) adapter (or equivalent) to hook up the Mini DisplayPort head. You may also need to hook up the USB head.

Yes, the TB3-to-TB2 adapter will work.

Remember that the US$50 Thunderbolt-2 <-> ThunderBolt-3 adapter supports ONLY genuine Thunderbolt devices, and no other sorts of devices. In addition, it does not pass Power across the interface. You also may need an additional other cable on one side or the other, depending on what you are adapting.

dkcrystal wrote:

Thanks - I’m still confused because the article suggested below seems to say I need USB C adaptor for 2025 MB air - though Apple say TB4 and USB C are not the same.

USB-C is just a flexible connector – it's like the concept of a Swiss Army knife.  Some particular USB-C ports may have very few "blades".  Those on docks are often only for plugging in a power brick, or for plugging in accessories that need USB 2/3 data.

Others may have a lot of blades.  Just about all Mac USB-C host ports have "blades" for USB 2/3, DisplayPort Alt Mode, Thunderbolt, and (on Apple Silicon Macs only) USB4. Those on Mac notebooks can also accept charging power. Apple likes to call these multi-purpose ports "Thunderbolt ports" or "Thunderbolt / USB4 ports" as a way of emphasizing that they are not bare-bones ports, and have desirable features.

E.g., the Technical Specifications for the M4 MacBook Airs say that they have

Two Thunderbolt 4 (USB-C) ports with support for:

Charging

DisplayPort

Thunderbolt 4 (up to 40Gb/s)

USB 4 (up to 40Gb/s)

There are a few Mac USB-C ports that are not Thunderbolt ports:

• The 12" Retina MacBooks that Apple released between 2015 and 2017 had a single USB-C port that supported USB, DisplayPort, and charging – but not Thunderbolt.
• The front-panel USB-C ports on Mac Studios with (M1/M2/M4) Max chips are USB-only.
• The front-panel USB-C ports on (M4 / M4 Pro) Mac minis are USB-only.

You can't use these ports to drive a Thunderbolt Display, and you can't use the front-panel USB-C ports on these particular Mac Studios and minis to drive any display.

You might additionally find something useful in this article:

About the Apple Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter - Apple Support

Welcome to the often-confusing world of USB.

Technically, USB-C only defines the physical interface.

Thunderbolt meanwhile defines one (of several) groups of signaling and power-delivery characteristics which can run across that interface.

Restated: All TB3 and TB4 cables will use a USB-C interface; but not all “USB-C” cables will support TB.

and it’s closely-related corollary:

Not all USB-C cables are “created equal”

Clear as mud ???