Changing Your Startup Drive

Dan Knight - March 1998, updated Dec. 2001

How can I force my Mac to boot from a different hard drive?

The best option is to use the Startup Disk control panel - but sometimes you can't get there because the internal drive is set as default, and that drive has a problem.

Be sure to try booting with extensions off. Sometimes that will let you get around a software problem so you can use the Startup Disk control panel.

If not, hold down Command-Option-Control-Shift while booting. This combination is built into the Mac ROMs and makes Macs boot in the default sequence of the Mac Plus (which doesn't support the Startup Disk control panel). This key combination forces your Mac to scan the SCSI bus in this order: 6, 5, 4, 3, 2, 1, 0.

If there is a bootable drive or partition available at a SCSI ID higher than 0 (or the ID of your troublesome drive), this will let you boot from it. I can't say how this works with Macs using IDE/Ultra ATA drives; I've never tried it.

Failing this, you may need to use a boot floppy, Disk Tools disk, or boot from CD-ROM. Macs with internal floppies will boot from the floppy drive if a bootable disk is present at startup.

Booting from CD-ROM requires an Apple CD-ROM player or a third-party player that uses the Apple drivers, a Centris 610 or newer, and a SCSI ID of 3 for the CD-ROM drive. Holding the C key during startup forces these computers to check the CD-ROM for a bootable disk.

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