Does Windows 10 Duel Boot affect the mbr of another drive?

[Flybye]

Say I have a fully functioning copy of Windows 7 on Drive A. I Want to install Windows 10 on Drive B to test on. Setting up where to install Windows 10 during the setup is pretty easy. What I would like to know is if I use Windows 10 boot utility to choose between Windows 10 or 7, would it affect the mbr on Drive A? If things don't work out as expected with Windows 10, I would like to be able to just disconnect Drive B and boot up into Windows 7 without having to do any repairs on Drive A to make it bootable again.

Edit: Ah general consensus is to be safe and just select the boot drive from bios like I always have.

 

[BinarySynapse]

Disconnect any drives you don’t want Windows to modify. Windows will modify the BCD store on the volume it determines the system will boot from so that it points to the new installation. (It might create an option to boot from the previous installation, though. I can’t quite remember.)

If it doesn’t find an existing BCD store, and your booting in UEFI mode, Windows will create a new UEFI boot entry, replacing anything that might have been there before.

 

[JustinC]

It most definitely affects the MBR of the other drive.
I think you should use EasyBCD.
First, install Windows on the required drive and do that after disconnecting all of the other drives.
Then install the other OS and use EasyBCD to alter the boot order.