How to Boot a Mac in Target Disk Mode

Target Disk Mode is a very handy feature available to use with Mac’s that have Firewire or Thunderbolt ports, and it allows you to use one Mac as an external drive on another host machine. This incredibly useful feature makes troubleshooting, installations, large file transfers, and critical backups extremely easy and very fast.

Before beginning, be sure both Mac computers have Firewire or TB ports, and that you have a Firewire or Thunderbolt cable. Each Mac must use the same port, for example, if you’re booting target disk with Thunderbolt, both Macs must use thunderbolt. A converter may work, but it is not recommended.

How to Use Firewire or Thunderbolt Target Disk mode

• Turn off the ‘target’ Mac (the one who’s drive you want to show up on the host)
• Now connect both Mac’s to each other with the Firewire or Thunderbolt cable
• Boot the target Mac while holding down the ‘T’ key until you see a Firewire or Thunderbolt icon displayed on screen, this signifies that target disk mode is detected and working
• In a few moments, the Mac will bot as usual and the target Mac’s hard drive should appear on the host Mac’s desktop, allowing you to access it like any other external drive
• When you are finished, safely eject the target Mac as if it’s any other disk

Once the target Mac has been ejected and disconnected it can be used as normal.

I use Target Disk Mode constantly, it’s ridiculously fast and an excellent method to transfer giant files, but it’s also amazingly useful for troubleshooting problematic Macs and performing some last minute backups of critical files and data if a computer is on its last legs. Though Firewire is no longer shipping on Macs, thankfully Firewire was replaced with Thunderbolt as a high speed data connection on newer machines, which allows this feature to carry on, and that’s so much better than removing the Target disk feature completely. And no, for the record, you can’t use Target Disk Mode with USB, for now at least, though you can boot from an external USB drive or flash drive if necessary, just not in target mode like this.