How to Use Target Disk Mode to Boot From Another Mac’s Hard Drive

| MGG Answers


Ken writes: I need to set up and configure a new Mac mini but I don’t have the space at my desk to hook up a monitor, mouse, and keyboard. I work daily with my MacBook Pro; is it possible boot the Mac mini with the MacBook Pro and use the laptop’s display, keyboard, and trackpad to control the mini?


The answer to your question arrives courtesy of a feature called Target Disk Mode (TDM), which Apple introduced way back in 1991 with the PowerBook 100. TDM allows a user to connect two Macs using either FireWire or Thunderbolt, allowing one Mac to access the other’s internal drives as if they were external FireWire or Thunderbolt drives.

TDM is most often used to help diagnose malfunctioning Macs. If a Mac won’t boot, a user can connect it to a working Mac, initiate Target Disk Mode, and then, if the hard drive is still functioning, view the drive’s contents. From a user perspective, the internal drives of a TDM-connected Mac appear indistinguishable from those of an external drive enclosure.

But an even more interesting aspect of TDM is that it allows a user to view another Mac’s hard drive as a potential boot drive, and to boot natively into OS X with a combination of one computer’s hardware and another computer’s software. In Ken’s situation, he would put the Mac mini into Target Disk Mode, attach it to his MacBook Pro using FireWire or Thunderbolt, and then boot the MacBook using the mini’s hard drive, producing the same basic result as if he had physically removed the mini’s drive and installed it in his MacBook.

To accomplish this, first make sure that your “target” Mac (the one you’ll configure for Target Disk Mode) is running a version of OS X equal to or greater than the “host” Mac. As you may know, with very few exceptions, Apple does not update older versions of OS X to support newer hardware. So if your host Mac is a new 2013 Haswell-based MacBook Air, for example, and your target Mac’s hard drive has OS X 10.7 Lion installed, you won’t be able to boot to the target hard drive because Lion doesn’t possess the drivers for the new Haswell hardware.

Assuming that your Macs are compatible, next decide if you’ll use Thunderbolt or FireWire. If available, Thunderbolt will provide the fastest experience, especially when used with Macs that have internal solid state drives instead of mechanical hard drives. With Thunderbolt a relatively new addition to the Mac, however, you’ll likely find that FireWire is far more ubiquitous. Note that TDM will still work if you have to use a FireWire adapter, such as when connecting a 2010 MacBook Pro’s native FireWire 800 port to a 2013 MacBook Air using a Thunderbolt-to-FireWire adapter.

Mac Target Disk ModeIn our example, we'll use a 2012 Retina MacBook Pro (left) as the host to boot a 2011 MacBook Air (right) as the target.

Once your Macs are connected, shut them both down. Next, power on the “target” Mac (in Ken’s case that would be the Mac mini) and immediately press and hold the “T” key on the keyboard until you see a gray screen with a floating FireWire or Thunderbolt logo (depending on the connection type). For Ken’s Mac mini, which lacks a built-in keyboard, this means that he’ll have to at least temporarily connect a USB or Bluetooth keyboard to initiate TDM.

Target Disk Mode MacAfter booting the target Mac while holding the "T" key, the MacBook Air's hard drive appears as a bootable option on the Host MacBook Pro.

Now head to your “host” Mac, power it on, and press and hold the Alt/Option key on the keyboard until you see the OS X boot manager. This screen allows users with multiple internal or external hard drives to manually boot to a specific drive. Since the target Mac is in TDM and connected to the host Mac, the target Mac’s internal drive will appear in this list. Use the arrow keys or mouse cursor to select the target Mac’s drive and press Return to begin the boot process.

Target Disk Mode MacThe Host MacBok Pro is now booted, using the host's hardware to run the target MacBook Air's boot drive.

Your host Mac (in Ken's example, his MacBook Pro) will now boot up as if it was the target Mac (again, for Ken, the Mac mini). Although displayed and controlled via the MacBook’s hardware, the software and operating system will all be from the mini, which is now basically the world’s most expensive external drive. Ken is now free to install software, configure settings, and perform updates to the Mac mini, without having to set it up as a separate workstation on his small desk.

When you’re ready to disconnect the Macs, first shut down the host Mac. Then press and hold the power button on the target Mac to turn it off and remove the cable connecting the two computers.

This question was originally answered on MGG 469: Get Your Own Email Domain, Save a Headache

About MGG Answers:

Each week Dave Hamilton and John F. Braun provide some great troubleshooting advice to listeners of the Mac Geek Gab podcast. Here with MGG Answers we share some of those tips with the rest of the world!

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Of course, you do need at least a keyboard. Otherwise you can’t get the Mini into TDM.

Michael Johnston

SUCH an awesome and indispensable tip! It’s one of the most useful tools I have in my Mac repair belt and I don’t even have to carry it with me.


I have been wondering for years why can´t this be accomplished for USB….



TDM doesn’t work for USB cause as I understand it, USB relies on the CPU to handle I/O


Thanks for the asnwer, furbies. You mean Target Disc Mode doesn’t rely at all on the CPU?


@ trifero

AFAIK Target Disk Mode doesn’t require the CPU in the same way as USB does.

Doc Rock 1

OK I don’t understand.. if the target mac won’t boot, just how are you supposed to get it to enter target mode? Mine does, but my backlights appear burned out, and it is this one that has the harddrive I need to access, without all the major hassle of removing it from the iMac. Not a simple procedure like a tower, for instance..
Could you clarify how to access a drive on a mac that won’t boot, and how to access Target on a mac one cannot see the display on?


Target disk mode dow not require a working CPU. There is hardware on the board that routes the firewire directly to the disk.  Also works with the Thunderbolt connectors. To fire up the computer in target mode just hold down the T key while booting.  The computer so booted will be a firewire volume.  Plug in a cable and the working computer can see the disk on the disabled computer.

Just today I had put a new 1TB SSD/HD hybrid disk in a MacBook Pro.  The NetBoot process (Holding command-R while booting) did bring up the process to use the local WiFi to connect, but it didn’t go further.  I then started up the laptop in Target Disk mode.  The OS complained it couldn’t read the drive. I then used Disk Utility to create a single partition drive on the laptop. I rebooted the laptop in NetBoot mode, and now it is loading up nicely.

Target Disk mode is very helpful when dealing with a bad situation.  The ditto utility is pretty good about pulling data off a dying computer drive. In such a case, be sure to use sudo when invoking ditto.

From my experience I was surprised that formatting the disk was needed.  I would have thought that the NetBoot would have allowed DiskUtility to format the new drive. 

You can buy a USB to SATA cable.  Really handy to have to format new drives or to salvage old ones.  I didn’t think to format my drive beforehand.  If it weren’t for Target disk mode I would have had to remove the disk and format it.  With Target disk mode I was able to format it in place. 

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