When Apple dropped the SCSI interface, starting with the AGP Power Mac G4 and “Pismo” PowerBook G3 FireWire Target Disk mode replaced the earlier disk mode implementation, also receiving official support beyond laptops to all subsequent Macs with built-in Firewire. 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 all internal drives on the chain can be set to different IDs than the active host system's devices. Officially reserved for Apple's portables only, all PowerBooks exclusively supported disk mode except the 140, 145, 145B, 150 and 170. 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. This also made it possible to select the disk in the Startup control panel and boot up from it. A unique system control panel on the PowerBook was used to select a non-conflicting SCSI ID number from the host Mac.

Originally called SCSI Disk Mode, a special cable ( SCSI System Cable) allowed the original PowerBook series to attach to a desktop Mac as an external SCSI disk.

As long as the requisite software appeared in the system ROM, the Mac could be booted into disk mode. Neither supports USB however, Thunderbolt-to-Firewire, Thunderbolt-to-Gigabit-Ethernet, and USB-3.0-to-Gigabit-Ethernet adapters are an option when one of the computers does not have Firewire or Thunderbolt.Īpple introduced disk mode access with the original PowerBook 100 and continued to offer it with most subsequent PowerBook series and FireWire-equipped Macs. Migration Assistant supports Ethernet (wired) or Wi-Fi, which TDM does not. Target Disk Mode is the preferred form of old-computer to new-computer interconnect used by Apple's Migration Assistant. Target Disk Mode is useful for accessing the contents of a Mac which cannot be booted from its own operating system.

Some computers will also make their internal CD/DVD drives and other internal and external peripheral hardware available to the host computer. Hard drives within the target Mac, for example, can be formatted, partitioned, etc., exactly like any other external drive. Instead, the Mac's firmware enables its drives to behave as a SCSI, FireWire, Thunderbolt and/or USB-C external mass storage device.Ī Mac booted in Target Mode can be attached to the port of any other computer - Mac or PC - where it will appear as an external device. When a Mac that supports Target Disk Mode is started with the 'T' key held down, its operating system does not boot. Target Disk Mode (sometimes referred to as TDM or Target Mode) is a boot mode unique to Macintosh computers.

How to exit target disk mode