How do I use my Mac as an external hard disk for another computer?

To make a Mac act as an external hard disk, you can put it in Target Disk Mode and connect it to another Mac with a FireWire cable, as follows.

Note: Target Disk Mode is available on most Macintosh computers produced in 2000 or later, as well as a few older models. More recent computers that do not have FireWire ports are excluded.

1. Shut down the computer you want to use as an external hard disk (i.e., the target computer). If you are using a portable computer, make sure it is running on AC power. You don't need to power down the other computer (i.e., the host computer).
   
   
2. Unplug all FireWire devices from both computers. Connect the FireWire cable to the FireWire port of the target computer, and then connect the other end of the cable to the host computer's FireWire port.
   
   
3. Start up the target computer and hold down the letter  t  on its keyboard. Its drive will spin up, and its icon should appear on the host computer. The target computer's display will show a moving FireWire icon. You may re-attach other FireWire devices now and use the target computer as an external hard drive.

Alternatively, in Mac OS X 10.4 and later:

1. From the Apple menu, select System Preferences... .
   
   
2. In System Preferences, from the View menu, select Startup Disk.
   
   
3. In the Startup Disk preference pane, click Target Disk Mode... .

To exit FireWire Target Disk Mode, on the host computer, drag the target computer's disk icon to the Trash, and then shut down the target computer. Disconnect the FireWire cable, and then start up the target computer; it will boot normally.

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