Target Disk Mode

Target Disk Mode (sometimes referred to as TDM or "Target Mode") is a boot mode for Macintosh computers wherein the Mac does not load the operating system, but instead behaves as a FireWire mass storage device with the SBP-2 (Serial Bus Protocol) standard. "Target Disk Mode." "Developer Connection". 16 Jan. 2002. Apple Computer Inc. 13 Jul. 2007. ]

When booted to TDM, all of the computer's attached volumes (HFS+ volumes, MS-DOS volumes, DVD-ROM, etc.) appear as devices attached to the hub. It is possible to daisy chain several Macs together by booting them each to Target Disk Mode. All of the volumes on all of the computers will be available to the host computer at the end of the chain.

Target Disk Mode is the preferred form of old-computer to new-computer interconnect used by Apple's Migration Assistant.

History

Apple introduced disk mode access with the PowerBook 100 and continued to offer it with most of the subsequent PowerBook series and Firewire equipped Macs. As long as the requisite software appeared in the system ROM, the Mac could be booted into disk mode.

Originally called SCSI Disk Mode, a special cable allowed the original PowerBook series to attach to a desktop Mac as an external SCSI disk. A unique system control panel on the PowerBook was used to select a non-conflicting SCSI ID number from the host Mac.

With the change to IDE drives starting with the PowerBook 150 and 190, Apple implemented HD Target Mode, which essentially enabled SCSI Disk Mode by translating the external SCSI commands via the ATA driver. Officially reserved for Apple's portables only, all PowerBooks exclusively supported disk mode except the 140, 145, 145B, 150 and 170. However, SCSI Disk Mode can be implemented unofficially on any Macintosh with an external SCSI port, by suspending the startup process with the interrupt switch, as long as its internal drive can be set to a different ID than the active host System's devices.

When Apple dropped the SCSI interface starting with the PowerBook G3, Firewire Target Disk mode replaced the earlier disk mode implementation. Further, TDM now officially supports all desktop models as well as the portable lines, if equiped with Firewire ports. In addition to the previously mentioned 68K PowerBooks the only Macs which do not provide for any kind of disk mode (supported or otherwise) are the original iMac and iBook series, as well as the new MacBook Air.

Using Target Disk Mode

Target Disk Mode is activated by holding the T key on the keyboard immediately after powering on the computer. The Target Disk booted computer is then plugged into a host computer or other device via a FireWire cable. To shut it down, you simply eject the volume(s) from the host computer and then press the power button again on the system that was in Target Disk Mode; that system will immediately power down.

Requirements for Target Disk Mode

Host computer requirements

The host computer (the computer into which the Target Disk Mode booted computer is plugged) must meet the following requirements:
* Built-in FireWire port, or a FireWire port on a PC card
* FireWire 2.3.3 or later
* Mac OS 9 or later
* Microsoft Windows, but with some issues - To read a Mac's HFS formatted disks, extra software is necessary. With MediaFour MacDrive Media, people have been able to successfully read and write from Windows onto HFS+ filesystems including using macbooks using target-mode. (some have been able to fix connection issues on Windows' 1394 ports using this method: uninstalling the 1394 host device- the device which controls the 1394 ports on the Windows PC for firewire, from the Windows device manager, and then reinstalling it). MediaFour MacDrive also has a read-only software switch to prevent any accidental write such as Windows writing $RECYCLED or other default root system folders.

Compatible computers

* eMac (all models)
* iBook (FireWire) and all models introduced after September 2000
* iMac (Slot Loading) with Firmware version 2.4 or later
* iMac (Summer 2000) and all models introduced after July 2000
* Mac mini (all models)
* Mac Pro (all models)
* MacBook (all models)
* MacBook Pro (all models)
* Power Mac G4 (AGP Graphics) with ATA drive
* Power Mac G4 (Gigabit Ethernet) and all models introduced after July 2000
* Power Mac G4 Cube
* Power Mac G5 (all models)
* PowerBook G3 (FireWire)
* PowerBook G4 (all models)

"Note that this list includes all Macintosh computers introduced after July 2000, excluding only the MacBook Air."

Similar utilities

On a non-Macintosh computer, the users can often share their internal drive using a Live CD, such as BART PE or Knoppix. This is not as convenient, but provides the means to copy files off an internal drive even if that drive does not contain a bootable operating system.

Notes