What Is an Active Partition?

An active partition is a hard disk drive (HDD) or a solid-state drive (SDD) partition designated in the partition table as bootable and containing the computer's primary operating system. Each drive can have only one active partition.

In Windows, only the primary partitions (the first four partitions) can be active. On Linux, bootloaders such as GRUB allow booting a system from non-active partitions.