How-To How to enable Target Disk Mode via Thunderbolt Target Disk Mode is a feature that allows a Mac to act as an external hard drive.

I followed the drill and tried to create USB boot media using 10.12 and 10.13 but the multiple attempts failed. I was working with someone on IRC who does this all the time and it was baffling.

Step 2: Boot into Target Disk Mode on the old Mac Shut down the old Mac that will be receiving the hard drive cleaning, and reboot it while holding down the "T" key on your keyboard.

If your Mac is having problems, macOS has multiple keyboard combinations that you can hold to recover your system, start in safe mode, run diagnostics, and more. Here's how to use them.

Since the release of the Intel Mac computers [and well beforehand -- see update above], and with Mac OS X 10.4.5 or later, you can start up from an installed system on a USB hard disk.

Target Disk Mode allows you to quickly share files between two MacBook Pros using Thunderbolt 3. Watch our video walk-through as we guide you through the process step-by-step.

If you have a Bluetooth keyboard, OS X may ignore keystrokes at startup for booting into Safe mode and other optional boot environments.