Connect your computers with the correct cable
Identify the ports on both Mac computers so that you can choose the correct cable. Target disk mode works when your computers are connected to each other using any of these ports:
- Thunderbolt 3 (USB-C)
- Thunderbolt 2
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.
If one or both computers has a Thunderbolt 3 (USB-C) or USB-C port, you can connect them as follows:
- To connect a Thunderbolt 3 (USB-C) port to either 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 either 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 Adaptor 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 Mophie USB-A Cable with USB-C Connector.
Start up in target disk mode
Take either of these steps on the Mac you want to use as the external hard disk:
- Turn on the Mac and immediately press and hold the T key while it starts up.
- If the Mac is already turned on, choose Apple menu > System Preferences and then click Startup Disk. Click Target Disk Mode, then click Restart when you're asked to confirm.
When your Mac enters target disk mode, it displays a large Thunderbolt , USB or FireWire symbol onscreen. If your computers are connected to each other correctly, the Mac in target disk mode should now be available as a disk on the other Mac. Use it as you would use any other disk.
To exit target disk mode, first eject the disk from the other Mac. For example, select the disk and then choose File > Eject. Or just shut down the other Mac. Then press and hold the power button for up to 10 seconds on the Mac you're using as a disk. Release the button when the Mac turns off.
If the target disk doesn't appear on the other Mac
If the Mac 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.