Which partition to make active?

In Windows 10 "Disk Management" I accidentally change the active partition to another drive and now I can not remember which one should be active. My C:\ is an SSD has 4 partitions:

System reserved 500MB
C:\ drive
100GB unallocated for provisioning
470MB recovery partition

Now should I make C:\ partition active or the partition labeled system reserved 500MB ?

1 Answer

The partition flagged "active" should be the boot(loader) one. That is, the partition with BOOTMGR (and the BCD) on it.

On a typical fresh Windows 10 installation, this would be the "System Reserved" partition, yes.

Of course, this only applies to MBR disks (booted in BIOS/CSM compatibility mode). GPT disks should instead be using a EFI System Partition, identified by the partition ID rather than any "active" flag. Windows can only boot GPT disks in UEFI mode.