I have two hard drives that have two different operating systems that operate independently.
What I normally do is open up my case and physically unplug current hard drive and plug the other one in when I want to switch between them.
Is there another way to do this without having to physically switch cables? I don't want dual boot it where it's on the same hard drive. I like the physical separation too and being able to work on them independent of each other.
Usually from the BIOS you can select from which device/drive to start from.
It is motherboard depending... but usually you can switch the order entering in the BIOS and saving the changes. You can even try to disable an HDD and hide it to the other operative system; I said you can try because some operative system can in some cases overcame this feature and see the HDD however.
Some BIOSes allow you, pressing a special combinations of keys, to enter in a reduced menu with only the list of devices from which you can boot, then you can select the one you prefer.
All depends from the couple of BIOS/Motherboard you have.
If you are only using windows, you can use BCD editor tools to set up which windows volume to boot from. You want to use something like this:
If any of you OSes are linux, or you simply want to use it (once set up it's quite nice), you can use GRUB from picking which boot volume you want to start up into. You can set it up with something like this:
