With Vista/7/8/8.1, having more than 1 HDD/SSD physically attached meant that the system partition(s) could potentially be on any disk. Is this still the case in 10, or has Microsoft finally fixed this bug?
Windows 10 setup normally only updates the boot files already contained on a system (if it finds any) rather than creating new ones. Windows 10 will install the operating system wherever you tell it to, but the boot files that load before the OS may be on a different HDD/SSD if they were preexisting.
A common occurrence is that someone will install a new hard drive for Windows 10 in addition to an old hard drive for Windows 7. They install Windows 10 onto the new hard drive, but Windows 10 doesn't create new boot files on the new hard drive, it updates the boot files on the old Windows 7 hard drive. The person then decides to "take the plunge" and format their old Windows 7 hard drive and the computer won't boot the next time because they just erased the boot files.
The way to be absolutely sure you know which drive the boot files are going to install to is to have only the drive connected that you want both Windows 10 and the boot files to be on when you install Windows.
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