How do I use my Macintosh as an external hard disk for another computer?

Whether or not you may use your Macintosh as an external hard disk depends on what model you have, and how the computer to which you want it to connect is equipped. There are two methods, one that uses FireWire and another that uses SCSI.

FireWire Target Mode

Models that you may use as an external disk in FireWire Target Disk Mode include: PowerBooks and iBooks with FireWire ports; the G4 Cube; the eMacs; Power Macs starting with the AGP-slot G4s; and iMacs, except for the G3 iMacs without slot-loading CD-ROMs. To use your FireWire-equipped computer as an external hard drive, the computer to which you wish to connect must have a FireWire port and be running Mac OS 8.6 or later. You must also have a 6-pin to 6-pin FireWire cable. To use FireWire Target Disk Mode, follow these instructions:

1. Shut down the computer you want to use as an external hard disk (i.e., the target computer). If you are using a portable computer, make sure it is running on AC power. It is not necessary to power down the other computer (i.e., the host computer).
   
   
2. Unplug all FireWire devices from both computers. Connect the FireWire cable to the FireWire port of the target computer, then connect the other end of the cable to the host computer's FireWire port.
   
   
3. Start up the target computer and hold down the letter  t  on its keyboard. Its drive will spin up and its icon should appear on the host computer. The target computer's display will show a moving FireWire icon. You may re-attach other FireWire devices now and use the target computer as an external hard drive.

Alternately, in Mac OS X 10.4 and later, you may restart the target computer in Target Disk Mode by following these steps:

1. From the Apple menu, select System Preferences... .
   
   
2. In System Preferences, from the View menu, select Startup Disk.
   
   
3. In the Startup Disk preference pane, click the Target Disk Mode... button.

To exit FireWire Target Disk Mode, on the host computer, drag the target computer's disk icon to the Trash, then shut down the target computer. Disconnect the FireWire cable, then start up the target computer, and it will boot normally.

SCSI Disk Mode or HD Target Mode

Note: SCSI Disk Mode and HD Target Mode function identically. The only difference is that some PowerBooks have SCSI disks while others have EIDE disks. For brevity, this document will use the term SCSI Disk Mode to refer to both.

All PowerBooks with SCSI ports (except the 140, 145, 145B, 150, and 170) support SCSI Disk Mode. However, if you have a Duo 230 or 2300, you must use it with its MiniDock. To use your SCSI-equipped PowerBook as an external hard drive, the computer to which you wish to connect must have an external SCSI port. You also will need the following items:

• An HDI-30 SCSI disk adapter cable, which plugs into the SCSI port of the PowerBook
  
  
• A SCSI system cable. If you already have SCSI devices attached to the computer for which the PowerBook is to be a hard disk, you do not need an additional system cable.
  
  
• A SCSI terminator. If you are connecting to a Macintosh IIfx, make sure you get a black terminator.

Once you have everything, follow these instructions:

1. If the hard drives of the PowerBook and the computer to which it is connecting have the same names, you must rename one of them. These names cannot be identical.
   
   
2. In the PowerBook or PowerBook Setup control panel, set the SCSI ID number. This can be any number from 1 to 6, but make sure the number you choose is not in use by another device in the chain.
   
   
3. Power down both computers and any other devices in the SCSI chain.
   
   
4. Connect the HDI-30 cable to the back of the PowerBook and connect the terminator to the end of the HDI-30 cable. Connect the HDI-30 cable with the terminator to the SCSI system cable if you have no other external SCSI devices, or to the last device in the SCSI chain if you do. The PowerBook must be the last device in the SCSI chain.
   
   
5. Once you connect the cables, power up the PowerBook by pressing the appropriate key. The drive will then spin up. If there are any other devices in the SCSI chain, power those up as well.
   
   
6. Power up the other computer. The PowerBook's hard drive should appear on its display, while the PowerBook's display will show a moving SCSI icon with the selected SCSI ID number. In SCSI Disk Mode, treat the PowerBook like an external hard drive.

To exit SCSI Disk Mode, power down the computer to which the PowerBook is connected, then shut down the PowerBook and all other devices in the SCSI chain. Disconnect the PowerBook from the disk adapter cable and the cable from the SCSI chain or the connected computer. When you power up the PowerBook, it will boot normally.

Also see:

• Why won't my PowerBook or iBook power up?