How do I set C:\ drive as active after marking my D:\ drive as active?

Question

Hi all I was reading through this article which warns us:

I was wondering what does it mean by "stop working" ? If I mark my D:\ drive as active, how will I be able to change it back to C:\ drive later?

Answer 1

To super-over-summarize, you can take that warning at face value. Whichever partition has the bootloader you want to use should be marked as active (it doesn't matter where the operating systems are, just where the bootloader is). There's never any reason to mark a different partition as active unless you want to use a bootloader from that partition.

If you render your machine unbootable in this way (by, say, setting a partition with no bootloader at all as active), you'll need to boot to a LiveCD or Windows repair environment or something like that (or slave the drive to another machine) to fix it. It's an easy fix but does require an environment to do it in.

Answer 2

When you boot your computer, it looks at the active drive to find the bootloader, which starts up the operating system. If your active drive is one which does not contain a bootloader, the operating system will be unable to start.