Target Disk Mode (sometimes referred to as TDM or Target Mode) is a

boot A boot is a type of footwear. Most boots mainly cover the foot and the ankle, while some also cover some part of the lower calf. Some boots extend up the leg, sometimes as far as the knee or even the hip. Most boots have a heel that is cle ...

mode unique to

Macintosh The Mac (known as Macintosh until 1999) is a family of personal computers designed and marketed by Apple Inc., Apple Inc. Macs are known for their ease of use and minimalist designs, and are popular among students, creative professionals, and ...

computers. When a Mac that supports Target Disk Mode is started with the 'T' key held down, its

operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs. Time-sharing operating systems schedule tasks for efficient use of the system and may also in ...

does not boot. Instead, the Mac's firmware enables its drives to behave as a

SCSI Small Computer System Interface (SCSI, ) is a set of standards for physically connecting and transferring data between computers and peripheral devices. The SCSI standards define commands, protocols, electrical, optical and logical interface ...

FireWire IEEE 1394 is an interface standard for a serial bus for high-speed communications and isochronous real-time data transfer. It was developed in the late 1980s and early 1990s by Apple in cooperation with a number of companies, primarily Sony an ...

Thunderbolt A thunderbolt or lightning bolt is a symbolic representation of lightning when accompanied by a loud thunderclap. In Indo-European mythology, the thunderbolt was identified with the 'Sky Father'; this association is also found in later Hell ...

, or

USB-C USB-C (properly known as USB Type-C) is a 24-pin USB connector system with a rotationally symmetrical connector. The designation C refers only to the connector's physical configuration or form factor and should not be confused with the conne ...

external

mass storage device In computing, mass storage refers to the storage of large amounts of data in a persisting and machine-readable fashion. In general, the term is used as large in relation to contemporaneous hard disk drives, but it has been used large in relati ...

. 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. Target Disk Mode is useful for accessing the contents of a Mac which cannot load its own

. Target Disk Mode is the preferred form of old-computer to new-computer interconnect used by Apple's Migration Assistant. Migration Assistant supports

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(wired) or

Wi-Fi Wi-Fi () is a family of wireless network protocols, based on the IEEE 802.11 family of standards, which are commonly used for local area networking of devices and Internet access, allowing nearby digital devices to exchange data by radio wave ...

, which TDM does not. Neither supports

USB Universal Serial Bus (USB) is an industry standard that establishes specifications for cables, connectors and protocols for connection, communication and power supply (interfacing) between computers, peripherals and other computers. A broad v ...

; 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.

History

Apple introduced disk mode access with the original

PowerBook 100 The PowerBook 100 is a portable subnotebook personal computer designed and manufactured by Sony for Apple Computer and introduced on October 21, 1991, at the COMDEX computer expo in Las Vegas, Nevada. Priced at US$2,500 with external floppy ...

and continued to offer it with most subsequent

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series and FireWire-equipped Macs. As long as the requisite software appeared in the system

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, the Mac could be booted into disk mode. Target Disk Mode was originally called SCSI Disk Mode, and a special cable ( SCSI System 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. This also made it possible to select the disk in the Startup control panel and boot up from it. 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, the mode was supported by all PowerBooks except the

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145 145 may refer to: *145 (number), a natural number *AD 145, a year in the 2nd century AD * 145 BC, a year in the 2nd century BC *145 (dinghy), a two-person intermediate sailing dinghy * 145 (South) Brigade * 145 (New Jersey bus) See also * List of ...

, 145B,

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and

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. However, SCSI Disk Mode can be implemented unofficially on any Macintosh with an external SCSI port by suspending the startup process with the

interrupt In digital computers, an interrupt (sometimes referred to as a trap) is a request for the processor to ''interrupt'' currently executing code (when permitted), so that the event can be processed in a timely manner. If the request is accepted, ...

switch, as long as all internal drives on the chain can be set to different IDs than the active host system's devices. 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.

supports Target Disk Mode. The 12-inch Retina MacBook (early 2015) has only one expansion port, a USB-C port that supports charging, external displays, and Target Disk Mode. Using Target Disk Mode on this MacBook requires a cable that supports USB 3.0 or USB 3.1, with either a USB-A or USB-C connector on one end and a USB-C connector on the other end for the MacBook. With the

Mac transition to Apple silicon The Mac transition to Apple silicon is the process of changing the central processing units (CPUs) of Apple Inc.'s line of Mac computers from Intel's x86-64 processors to Apple-designed systems on a chip that use the ARM64 architecture. CEO ...

, Apple replaced Target Disk Mode with Mac Sharing Mode.

System requirements

The target computer (the computer to be placed into TDM) must: * Have FireWire or Thunderbolt Port * Have an ATA device at ATA bus 0 * Be any Macintosh except the following models: ** iMac (Tray-Loading) **

Power Macintosh G3 (Blue & White) The Power Macintosh G3 (also sold with additional software as the Macintosh Server G3) is a series of personal computers designed, manufactured, and sold by Apple Computer from November 1997 to August 1999. It represented Apple's first step towa ...

** iBook G3 models without FireWire **

Power Macintosh G4 The Power Mac G4 is a series of personal computers designed, manufactured, and sold by Apple Computer from 1999 to 2004 as part of the Power Macintosh line. Built around the PowerPC G4 series of microprocessors, the Power Mac G4 was marketed by ...

(PCI Graphics) {{cite web , title=Power Mac G4 (Yikes!) , date=August 31, 1999 , url=http://lowendmac.com/1999/power-mac-g4-yikes/ , accessdate=2013-11-12 **

MacBook Air The MacBook Air is a line of ultrabook computers developed and manufactured by Apple Inc. It consists of a full-size keyboard, a machined aluminum case, and, in the more modern versions, a thin light structure. The Air was originally positioned ...

(2008-2010) ** MacBook (Unibody) The host computer (the computer into which the Target Disk Mode booted computer is plugged) merely needs to meet the same requirements as for any external mass storage device using the bus in question, and (if access to native Mac formatted partitions such as the boot volume is desired) support for the correct version of

Hierarchical File System Hierarchical File System (HFS) is a proprietary file system developed by Apple Inc. for use in computer systems running Mac OS. Originally designed for use on floppy and hard disks, it can also be found on read-only media such as CD-ROMs. HFS ...

. On Classic Mac OS, this means FireWire 2.3.3 or later and

Mac OS 8 Mac OS 8 is an operating system that was released by Apple Computer on July 26, 1997. It includes the largest overhaul of the classic Mac OS experience since the release of System 7, approximately six years before. It places a greater emphasis on ...

.6 or later are required to use a Firewire target. The host computer may run

Microsoft Windows Windows is a group of several proprietary graphical operating system families developed and marketed by Microsoft. Each family caters to a certain sector of the computing industry. For example, Windows NT for consumers, Windows Server for serv ...

, but with some possible shortcomings: to read a Mac's HFS-formatted partitions, extra drivers such as MacDrive, TransMac, MacDisk, or HFSExplorer are necessary. Users also must ensure their computer possesses appropriate interface hardware in order to physically connect to a Mac in Target Mode. MacDrive also has a read-only option to prevent any accidental editing of the computer in Target Disk Mode; however, this mode cannot be set after an HFS/HFS+ disk is mounted. With the addition of HFS drivers into Apple's Boot Camp, it has also become possible for Macs running

Windows Windows is a group of several proprietary graphical operating system families developed and marketed by Microsoft. Each family caters to a certain sector of the computing industry. For example, Windows NT for consumers, Windows Server for serv ...

to read (but not write) HFS partitions, without the purchase of software. Users have separated these drivers from the main Bootcamp install, and now also install on other Windows computers. Host computers running

Linux Linux ( or ) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, which ...

are also able to read and write to a Mac's HFS or HFS+ formatted devices through Target Disk Mode. It is working out-of-the-box on most distributions as HFS+ support is part of the Linux kernel. However these filesystems cannot be checked for errors, so for shrinking or moving partitions it is preferred to use Mac OS.

Notes

MacOS Macintosh platform