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 makes troubleshooting, installations, large file transfers, and critical backups extremely easy and very fast.
How to use Firewire or Thunderbolt Target Disk mode
* First, be sure both Mac’s have Firewire or TB ports and that you have a Firewire or Thunderbolt cable
* 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 icon
* In a few moments, the target Mac’s hard drive should appear on the host Mac’s desktop and you can access it like any other external drive
* When you are finished, safely eject the target Mac as if it’s any other disk
I use Target Disk Mode constantly, so it’s a good thing Firewire was replaced with Thunderbolt as a high speed data connection newer Mac rather than removing the Target disk feature completely. For the record, you can’t use Target Disk Mode with USB (at least for now).