Target disk mode can be useful when you need to move files quickly between computers, or get files from a Mac that doesn't have a working display. It requires two Mac computers that are connected by cable using any of these ports:
Connect your computers with the correct cable
Depending on which ports your Mac computers have, use a Thunderbolt 3, USB-C, Thunderbolt 2, or FireWire cable to connect them to each other. Target disk mode doesn't support connections that use an Apple USB-C Charge Cable, USB-A to USB-A cable, or Mini DisplayPort cable.
After you connect the computers, start up in target disk mode.
If you're connecting with Thunderbolt 3 (USB-C) or USB-C
If one or both of the computers has a Thunderbolt 3 (USB-C) port or a USB-C port, you can connect using one of these configurations:
- To connect a Thunderbolt 3 (USB-C) port to another Thunderbolt 3 (USB-C) port or a USB-C port, use the Apple Thunderbolt 3 (USB-C) Cable.
- To connect a USB-C port to another USB-C port or a Thunderbolt 3 (USB-C) port, use the Apple Thunderbolt 3 (USB-C) Cable.
- To connect a Thunderbolt 3 (USB-C) port to a Thunderbolt 2 port, use the Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter combined with a Thunderbolt 2 cable.
- To connect a USB-C port to a USB-A port, use a USB-A to USB-C cable that supports USB 3.0 or USB 3.1, such as the Belkin USB-A to USB-C Cable (USB 3.1).
Start up in target disk mode
Take either of these steps on the Mac that you want to use as a disk:
- Turn on the Mac and immediately press and hold the T key while it starts up.
- If the Mac is already turned on, you can instead choose Apple () menu > System Preferences, then click Startup Disk. Click Target Disk Mode, then click Restart when you're asked to confirm.
The Mac starts up in target disk mode, then appears as a disk on the other Mac. You can now use it as you would any other disk. To exit target disk mode, press and hold the power button on the Mac you're using as a disk. Then disconnect the cable.
If the target disk doesn't appear on the other Mac
If the Mac you started up in target disk mode doesn't appear as a disk on the other Mac, follow these steps to mount the disk:
- Open Disk Utility on the other Mac. It's in the Utilities folder of your Applications folder.
- If the connection between your computers is good and you followed the steps to start up in target disk mode, the target disk should appear as a volume in the Disk Utility sidebar. Select that volume, then choose File > Mount from the menu bar, or click Mount in the toolbar.
- If the target disk is FileVault-encrypted, you're asked to enter a password to unlock the disk and mount it. Enter the administrator password for the Mac that you started up in target disk mode.
The disk should now be mounted and available to your Mac. However, if it's formatted for APFS, your Mac must be using High Sierra or later. Earlier versions of the Mac operating system don't mount APFS-formatted volumes.
As an alternative to target disk mode, you can use AirDrop to send content between two Mac computers wirelessly.