Target Disk Mode
boot mode on certain Macintosh computers
Target Disk Mode (sometimes referred to as TDM or Target Mode, formerly SCSI Disk Mode) is a boot mode unique to Macintosh computers.
When a Mac that supports Target Disk Mode 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 Windows, 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.
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.
Begin with the source’s own compact description: “Target Disk Mode” is boot mode on certain Macintosh computers. The dossier treats that line as a proposition to test through Target, Disk and Mode, not as a finished interpretation.
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Named sources, stable identifiers and responsible institutions provide the strongest route from overview to verifiable evidence. The source revision retrieved here is dated Sep 17, 2026. The linked authority identifier is Q7685857. None of the 0 selected statements returned an explicit reference.
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This entry incorporates text from “Target Disk Mode” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.