I've run a dual boot setup for years, two drives for OS systems. In the BIOS you select the boot priority. Whatever is first boots up when you do nothing, and if I tap the F12 key while booting I can then select the boot drive.
Mostly I did this as I transitioned from XP to Win 7, then again from Win 7 to Win 10 with a clean install.
Very useful as sometimes for old projects I have to go back to the old OS to check what patch I may have used on Amplitube, or Dim Pro etc...
A Life saver actually!