Booting up and holding down 'option'

I learned that you can hold down the 'option'-key when powering up to select which drive you want to boot from if you for example have a CD in the CD-drive that contains an operating system and you want to boot from that. I'm not sure i'm posting this question in the right forum as this hasn't got anything to do with BootCamp or Parallels, but here goes:

Is it possible to use this method to boot up from an usb HD? So, if I've got another OS (Linux or Windows or whatever) on an usb HD I just plug in the external HD and hold down the 'option' key on start-up to choose this drive Anyone familiar with this?

Yes it's possible. It's one of those "at your own risk", but possible none-the-less.

Check these out.

http://www.mac-forums.com/forums/showthread.php?t=50499&highlight=bootable+ipod

http://www.mac-forums.com/forums/showpost.php?p=268391&postcount=2

RIDE said:

Yes it's possible. It's one of those "at your own risk", but possible none-the-less.

Check these out.

http://www.mac-forums.com/forums/showthread.php?t=50499&highlight=bootable+ipod

http://www.mac-forums.com/forums/showthread.php?t=43625&highlight=bootable+ipod

Click to expand...

Ok thanks! But how do you mean "at your own risk"? Is it risky if I've got an empty external HD?

I say that because the Ipod was not made to be a full-time drive for running an OS... The life-cycle on an iPod HD is rated at around 20,000 hours... The HD in your MacBook is rated at around 750,000 hours. The heat generated by running an OS could damage an ipod. I have also heard of someone getting Gray Screen/Static on their Macs, and having to boot from the install discs to get back to normal.

My GUESS is that if you boot from it every now and then, your not going to have any problem.

The above is just a disclaimer. Don't get me wrong... I plan on doing it, just haven't got around to it yet. The "at your own risk" should be applied anytime you are using something in a way that it was not meant to be used.

Ok I plan on using a 'normal' external HD (not an Ipod) so perhaps the external HD will be a bit more 'stable' in this matter...

It will be PERFECT!

If memory serves me right it has to be a firewire drive, because you cant boot from a usb one.

Intel machines can boot from USB, but PPC's cannot.