One of the simplest, least known about, and greatest tools IMO that Apple has ever made is Target Disk Mode. Target Disk Mode is a feature that allows your Mac to act as an external hard drive. This is the one area that I dream Windows would copy. Imagine you have a bad Operating System and can’t boot into Verbose or Normal Mode? Or a wicked nasty virus that wont allow your OS to function normally. You’d need a pain free way to get all of your important data off of the infected drive. Target Disk Mode can help.
Enabling Target Disk Mode in Mac OS
For this to work there are some caveats involved. First, you will need another “Host” Mac for the non-working “Target” computer to tether to via Firewire. So all you will need is two Apple computers that have OS 8.6 or greater, both with Firewire ports, and a Firewire cable. The Host computer should be turned on during this procedure while the Target computer will remain off until you have the Firewire cable connected to both. If either of these are a laptop, it is advisable to connect the AC adapter to avoid complications of premature power offs. Turn on the target computer while holding down the “T” key on the keyboard. If done correctly, you should see the following screen.
If you see this, then you should be ready to move on to the next steps. If not or you are having trouble entering Target Disk Mode, you can force your computer to boot into Target Disk Mode on its next boot up as long as you can access the OS by opening “System Preferences”, choosing “Startup Disk”, and selecting “Target Disk Mode.” You will have to be in OS X10.4 (Tiger) or later to see those options in that order. Reboot and it should go into Target Disk Mode automatically.
Now that we have our Target computer ready, what will we see on the Host computer? Just as if you are connecting a Flash drive or External HDD, you will have a small drive appear on either your Desktop or in the Doc at the bottom of your screen. After it has been initialized, you can enter it and copy over whatever information you would like to save. Your desktop will likely look similar to the second picture in that your main HDD will be at the top followed by the Yellow External HDD indicator with the Firewire symbol.
After you are done retrieving any and all data, make sure to eject the disk properly before pulling the Firewire cord to avoid data corruption. There are a number of ways to do so if you are not familiar, here is a list of the ways to eject a drive.
Target Disk Mode Summary
It was that easy to backup files and data from a failing OS. This is one of the options we used to use when dealing with a failing HDD on Macs as it doesn’t tax the drive quite as bad as running a full OS on it. It will not help in every situation especially if you have a dead HDD, then you are out of luck doing it this way. Data recovery software and centers would be your only bet. If you have any issues with entering Target Disk Mode or questions whether your Mac is up to the task, you can visit this article by Apple to see all of the fine point details. Entering this mode will not harm your drive or mess with your booting so if you want to try it out, give it a shot as the next time you power on your machine, it should attempt to boot up the OS.