1. I am looking for answers not opinions why I should do this, or what is the purpose, or for that mater your opinion. Just looking for the answer to this question. Here is what I want to be able to do. I have three hard drives in my mac pro, I want to be able to install OS X on all three of them, that is not a problem, here is the trick. I want to be able to switch between each hard drive operating system without re-booting my computer and changing the start-up drive. Is there any application or mod that I can do on my computer to have all three hard drive operating systems load at the initial boot of the computer and only the one I select be active? So that I can switch between each hard drive operating system without having to reboot my computer and setting it in the start-up system?