Booting a Mac using FireWire is a quite good thing if you are having issues at Mac Boot Screen or you want to run a Diagnostic or you want to access to Computer but can’t do it through itself. You can either Purchase a FireWire drive or a Hard Drive with FireWire connector or you can use MacBook as a FireWire, if it has an appropriate FireWire connector.
Use FireWire When Mac Won’t Boot on Its Own.
Locate the FirwWire port near a USB Port, it must be with Angled Corners on one side of port.
Connect your Mac With FireWire Drive.
Hold Down the “Option” Key as you Power-up the Macintosh.
Select the FireWire Drive from the List of Options.
Click the Right Facing Arrow to select the FireWire Drive and finish Booting.
Operate FireWire After a Normal Reboot:
Connect your Mac with FireWire after a Successful Boot.
Open finder Window to make sure that FireWire device is listed in your Devices.
Open System Preferences, and select “Start-up Disk”.
Select FireWire drive to boot with.
Now Click “Restart” to reboot your Computer using FireWire.