We have an embarrassment of riches when it comes to the number of ways we can move data between Macs. You can send files via AirDrop, attach them to an email message, put them in a Messages conversation, turn on and connect via File Sharing, or use Dropbox or iCloud Drive as an intermediary, to name just a few of the more obvious approaches.
But what if you have a lot of data—say tens or even hundreds of gigabytes—to transfer from one Mac to another? The techniques listed above might work, but it could be slow if you don't run out of space. If you had an external hard drive with sufficient free space handy, you could copy all the data to it from one Mac and then copy the data back off to another Mac. To cut the copy time in half, though, try Target Disk Mode instead.
What Is Target Disk Mode?
Target Disk Mode lets an Intel-based Mac act as an external disk for another Mac. Apple-silicon Macs use Share Disk in macOS Recovery instead. For Intel Target Disk Mode, use a Thunderbolt cable if either Mac runs macOS 11 or later. A USB-C connector alone does not establish compatibility.
Choose the method and cable for your source Mac before starting:
Intel Macs: The T-key Target Disk Mode instructions below apply to an Intel source Mac.
Check compatibility: The source Mac, macOS versions, and cable matter. Follow Apple's Intel Target Disk Mode instructions for your setup.
Speed: Because Target Disk Mode on modern Macs relies on a Thunderbolt connection, and you’re connecting one Mac directly to another, you’ll get the fastest transfer speeds in the fewest steps.
You can also use Target Disk Mode on an old Mac to set up a new Mac using Migration Assistant, repair its drive using Disk Utility, or possibly even boot another Mac with it. Booting one Mac from another in Target Disk Mode works best if the two Macs are of the same model and vintage and are running the same version of macOS, but it might work even if those facts aren’t true.
Apple silicon: Use Share Disk
Connect the Macs with a data-capable USB, USB-C, or Thunderbolt cable. Shut down the source Mac, hold its power button until startup options appear, then choose Options > Continue. In Recovery, choose Utilities > Share Disk, select the volume, and start sharing. On the other Mac, open Finder > Network, select the source Mac, choose Connect As > Guest, and connect. After copying, eject the volume and stop sharing. See Apple's Recovery guide.
Intel: Step-by-step instructions
For an Intel source Mac, follow these Target Disk Mode steps:
On the source Mac, either:
Restart the Mac, and once it starts booting, hold down the T key until you see the Target Disk Mode screen with a floating Thunderbolt logo.
Open System Preferences > Startup Disk, click the lock button and enter your administrator credentials, click Target Disk Mode, and then click Restart.
Connect the source Mac to the destination Mac with an appropriate cable. The source Mac’s drive appears on the destination Mac’s Desktop like an external hard drive. (If the source Mac is running macOS 10.15 Catalina, two drives will appear on the destination Mac’s Desktop: DriveName and DriveName – Data. The first is Catalina’s system volume; you’ll find all your files and folders on the Data volume.)
Move or copy files as desired.
When you’re done, eject the drive and then press and hold the power button on the source Mac for a few seconds to shut it down.
If you have hundreds of gigabytes to transfer and either of your Macs is a notebook, it’s best to connect it to power to avoid draining the battery before the copy finishes.
Minor Gotchas
Two things can complicate putting a Mac into Target Disk Mode: FileVault and a firmware password. Both are easily worked around so long as you know the password:
If the Mac is encrypted with FileVault, hold down the T key at startup like normal, but then enter the administrator password for that Mac to complete the switch to Target Disk Mode.
If the Mac has a firmware password, press the Option key while the Mac is starting up and enter the firmware password when prompted. Then press the T key to continue booting in Target Disk Mode.
Use a cable that supports data, not merely charging. For Intel Target Disk Mode with macOS 11 or later on either Mac, use Thunderbolt. Share Disk on Apple silicon supports a suitable USB, USB-C, or Thunderbolt data cable.
Despite these small caveats, Target Disk Mode is one of the unsung innovations that has made Macs easier to use for decades, and it’s well worth keeping in mind whenever you need to move lots of data between machines.
(Featured image by Adam Engst)