The system is dual booted. First partition on the SSD contains Windows 8.1 and the second partition holds Windows 7 Pro. Both were rescued from previous machines/disks which were, in various ways, dying. They were copied onto the SSdisk with a free partition software program. If you want, I'll tell you which. So, there has been no installing of any kind.
When I boot up Windows 8, it makes itself C:\ and the Windows 7 partition D:\
When I boot up Windows 7, it makes itself C:\ and the Windows 8 partition, you guessed it, the D:\ partition.
What I am aiming for is that when I boot up Windows 7, it assigns it self to the D-partition, and Windows 8 to the C-partition. Just like it is when Windows 8 is booted up.
What I tried: After booting up in Windows 7, use DISKMGMT.MSC to change the C-drive letter to "D", which for obvious reasons didn't work.
The motivation for this setup is that the propiety software I need for my job, runs better if it's like that and saves time. I got no IT helpdesk to call. Reinstalling is not an option, because of licensing.
To be clear: Now, both OSes boot up, and all programs work. I did use a BCD editing softwareprog to make it so.
When I boot up, I do get a Windows 7 type of menu, not a fancy blue graphicy Windows 8.0/8.1/10 type of menu.