The Mark Partition Active command lets you designate a basic primary partition as active. An active partition is the partition from which the computer starts up. The system partition or volume must be a primary partition that has been marked as active for startup purposes and must be located on a disk that the computer accesses when starting up the system. There can be only one active system partition at a time, which displays as Active in the status field.

The Mark Partition Active command can be used only on a basic primary partition, not on a dynamic volume.

The names commonly used for partitions or volumes containing the startup and operating system files are the system volume and boot volume respectively. The system volume refers to the partition or volume containing the startup files. The boot volume is a partition or volume that contains the operating system files. The boot volume can be (but does not have to be) the same as the system volume. The boot volume also cannot be part of a spanned, striped, or RAID-5 volume.