Not all USB-C ports on a Mac behave the same way, and that distinction can cause real headaches if you don’t know about it.
On Macs with Apple silicon, and Intel-based Macs with the T2 chip, Apple designates one USB-C port as the DFU (Device Firmware Update) port. For most everyday use, it functions like any other port. But there are specific situations where it matters.
When the DFU Port Causes Problems
The DFU port’s primary purpose is Mac firmware recovery, used in conjunction with another Mac running Apple Configurator. If you ever need to revive or restore a Mac’s firmware, you must connect a USB-C cable, not a Thunderbolt cable, to the DFU port specifically. That scenario is rare, but Apple has also documented a more common exception: when installing or updating macOS on an external drive, avoid connecting that drive to the DFU port. If you do, the installation may fail partway through, often with an unhelpful error message like “Some updates could not be installed” or “com.apple.OSInstallerSetup.error 702.” Once installation is complete, you can use any port.
Beyond external drive installs, unexplained errors with peripherals connected through a Thunderbolt dock can sometimes be resolved simply by switching to a different port.
How to Find Your Mac’s DFU Port
Apple maintains a support document listing DFU port locations by Mac model and generation. The location varies, and Apple provides no visual indicator on the hardware itself. Worth noting: users have found errors in that document before, so if you’re encountering unexplained failures, try a different port even if you think you’re already on the right one.
The Bottom Line
For routine use, connecting displays, drives, docks, and other peripherals, you don’t need to think about this. But if you’re setting up or updating an external boot drive, identify your Mac’s DFU port first and plug the drive into a different one. And any time a peripheral behaves unexpectedly, try a different USB-C port before assuming the cable, drive, or software is the problem. It’s a simple step that can save significant time on troubleshooting.
(Featured image by iStock.com/Milosz Deptula)
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