Boot Partition

Boot drive should be partitioned as follows to obtain bootable drive:
-*System partition should be first partition located on drive. There cannot be unallocated space or anything else in the first location.
-*System partition must be “hidden” and not have a drive letter assigned to it.
-*System partition must be marked “Active” and "Primary".
-Windows OS needs to be located in the second position located on drive. It doesn’t matter what drive letter or label is on the partition. This would normally be partition C:. It must be marked "Primary".

Aomei Backupper will automatically do all this when restoring “System” to beginning space on a drive (unallocated or not).

The *System partition is the fist place BIOS goes to determine if drive is bootable and if it is not at the start of drive space it won’t be read. The *System partition then tells BIOS where to locate the operating system (Win10, etc.)

On the drive that has been or is the boot drive the *System partition will have a status of “System”. The partition with the Win OS will have a status of “Boot”. That status will change automatically from one drive to another depending on which is used for startup.

Windows “Disk Manager” (diskmgmt.msc) can be used as a convenient way to determine and manipulate status as opposed to second party programs.