The user has the option at boot time to put the computer into a mode of operation called Target Disk Mode (TDM).
When the iMac is in Target Disk Mode and connected to another Macintosh computer by a FireWire cable, the iMac operates like a FireWire mass storage device with the SBP-2 (Serial Bus Protocol) standard. Target Disk Mode has two primary uses:
The iMac computer can operate in Target Disk Mode as long as the other computer has a FireWire port and either Mac OS X (any version) or Mac OS 9 with FireWire software version 2.3.3 or later.
To put the iMac into Target Disk mode, you restart the iMac and hold down the T key until the FireWire icon appears on the display. You then connect a FireWire cable from the iMac to the other computer. When the other computer completes the FireWire connection, a hard disk icon appears on its desktop.
If you disconnect the FireWire cable or turn off the iMac while in Target Disk Mode, an alert appears on the other computer.
To take the iMac out of Target Disk Mode, you drag the hard disk icon on the other computer to the trash, then press the power button on the iMac .
For more information about Target Disk Mode, see the section "Target Mode" in Technote 1189, The Monster Disk Driver Technote. For information about obtaining the Technote, see "Apple Technotes".