Thanks Angel for pointing me at this article, which I had read previously and which prompted my question because it didn't address the part I am not sure of - separate drives.
I want to install on a completely different drive, not the current Windows 10 drive. I understand that I can shrink the Windows system partition on the system drive to make space for the new OS and install it on the new partition. But I don't understand
what happens if I install the 2nd OS on another internal drive.
Does the Windows 7 installation automatically update the boot records so that on start up he dual boot menu is presented.
Paul