What happens when I mark a partition as active?

In the disk management If I right click on the C: drive there is a option Mark a partition as active.

What happens when I mark my C: drive partition as active ?

Solution 1:

The partition that has Windows on it is already marked active.

If you mark another partition active, it will mark all other partitions as not active. If you reboot your computer with the Windows partition mark not active, it will not boot into Windows; it will probably say OS not found.

Unless you feel comfortable with the partitioning, formatting and installing files, I suggest that you leave the modifications to someone with more experience.

Solution 2:

Be careful to active partition. On MBR disk, the system reserved partition is required to be active. If you mark C: active, Windows will be unbootable. On GPT disk, the Mark Partition as Active option in Disk Management is grayed out. You can search accidentally marked drive C: active in google to find more details.