Target Disk Mode
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Target Disk Mode (sometimes referred to as TDM or Target Mode) is a boot mode unique to Macintosh computers.
When a Mac that supports Target Disk Mode[1] is booted with the 'T' key held down, its operating system does not load. Instead, its firmware enables the computer's drives to behave as FireWire mass storage devices.
A Mac booted in Target Mode can be attached to the FireWire port of any other computer - Mac or PC - where it will appear an external FireWire device. Hard drives within the target Mac, for example, can be formatted, partitioned, etc., exactly like any other external FireWire drive.
Target Disk Mode is useful for accessing the contents of a Mac which cannot be booted from its own operating system. Target Disk Mode is the preferred form of old-computer to new-computer interconnect used by Apple's Migration Assistant.
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[edit] 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 equipped 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, the MacBook Air, the late-2008 aluminium MacBook and the the late-2009 MacBook, all of which also lack a FireWire port.
[edit] Requirements for Target Disk Mode
[edit] 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 (either 400 or 800), or a FireWire port on a PC card
- FireWire 2.3.3 or later [1]
- Mac OS 9 or later [1]
- An ATA hard drive at ATA bus 0 [2].
The host computer may run 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--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.
[edit] 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 (original white and black plastic models, not the aluminum or plastic unibody 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 MacBooks with no FireWire port – the MacBook Air and some MacBooks (13-inch, Aluminum, Late 2008 and the 2009 plastic unibody).
[edit] Notes
- ^ a b c "Target Disk Mode." Developer Connection. 16 Jan. 2002. Apple Computer Inc. 13 Jul. 2007. <http://developer.apple.com/documentation/Hardware/Developer_Notes/Macintosh_CPUs-G4/PowerMacG4_16Jan01/3Input-Output/Target_Disk_Mode_.html>
- ^ "FireWire Target Disk Mode: Target Computer Shuts Down at Startup" Apple Computer support article: TA25584, last modified: June 12, 2002 [1]
