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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 ?

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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.

  • The C:\ drive labeled "boot" but it is not this partition it should be the "system reserved" labeled "System" ? – Welliam Mar 19 at 0:32
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    @Welliam The "boot" label in Disk Management is a lie. The only way to be completely sure is to mount the partition and check for a BOOTMGR, though 9 times out of 10 you can guess it's just the System Reserved partition. In the event that you do end up setting the wrong partition, this can be fixed by booting from a Windows install DVD/USB and using diskpart from the command prompt it provides. Automatic boot repair might also fix it. – Bob Mar 19 at 0:41

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