One of the implementations of Open Firmware, or EFI on Intel Macs, is the ability to select what local boot device you want to use at startup. This can be useful for troubleshooting startup or software issues by bypassing the local hard drive or OS and booting off a extra internal or external drive.
To Use Disk Selection Mode:
- Press the power button on the Mac.
- Immediately hold down the Option key.
- You should see a blue screen with a ‘refresh’ button and a ‘next’ arrow button. You’ll probably see a hourglass while the machine searches for bootable volumes. It will search all local hard drives, all CD/DVD drives, and all connected Firewire drives (Also USB for the Intel Macs.)
- Select the one you want by clicking on it once with the mouse.
- Click the ‘next’ arrow button. The mac will now attempt to boot off of that volume.
Important Notes
This will only change the boot device once. To permanently change the boot device, use the Startup Disk Preference Pane in System Preferences. This mode is disabled with an Open Firmware password is in place