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. 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.