I accidentally deleted 16 MB Microsoft reserved partition. PC didn't Boot after then. It was stuck without booting saying "unable to mount boot volume". I somehow managed to fix it by rebuildbcd. And now, it's booting fine. Now that 16mb partition is "unallocated". Do I need to do Anything? What was that 16mb partition? It wasn't the EFI partition. My efi partition is 256mb. Thanks!
it's Microsoft reserved partition (MSR) Beginning in Windows 10, the size of the MSR is 16 MB. The default partition layout for UEFI-based PCs is: a system partition, an MSR, a Windows partition, and a recovery tools partition.
If it's working then don't bother but next time make make sure you clean install Windows fomr a USB and on the installation screen delete all the partitions belonging to Windows and let them be created again.