Target Disk Mode

Apple G3 iMac booted in Target Mode

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 started with the 'T' key held down, its operating system does not boot. Instead, the Mac's firmware enables its drives to behave as a SCSI, FireWire, Thunderbolt, or USB-C external mass storage device.

A 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. Hard drives within the target Mac, for example, can be formatted or partitioned exactly like any other external drive. Some computers will also make their internal CD/DVD drives and other internal and external peripheral hardware available to the host computer.[2]

Target Disk Mode is useful for accessing the contents of a Mac which cannot load its own operating system. Target Disk Mode is the preferred form of old-computer to new-computer interconnect used by Apple's Migration Assistant. Migration Assistant supports Ethernet (wired) or Wi-Fi, which TDM does not. 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.

  1. ^ Apple Inc (16 January 2002). "Target Disk Mode". Apple Developer Connection. Retrieved 13 July 2007.
  2. ^ Griffiths, Rob (March 27, 2007). "Borrow an optical drive from another Mac". Macworld. Retrieved October 21, 2023.