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Active partition

The term active partition is relevant only for MBR partitions and booting by BIOS.

The active partition is the partition on the first hard disk which is automatically booted when no boot manager is installed. The partition marked as active is set in the partition table of the MBR. Please note that there is only one active partition allowed on each hard disk. If a boot manager is installed it is irrelevant which partition is marked as active, since the partitions are selected and booted from the boot manager.