You can you use Partion Magic (PM) or usual Dos OS. In PM when you right click on the partion there is an option make the partion active. in Dos, when it's running, write fdisk, and you will see the option to make your a partion active.
The system partition(a partition where the operating system is installed) is the active partition of the Hard Drive
By default C: is the active partition of the hard disk drive
The active partition is the partition which is marked as Active in Index table. the status and locations of partitions are stored in MBR(master boot record). The active status tells the system which partition to boot from. System boots from the partition which contains the Operating System(windows XP, 2003.....). So the partition which contains the Operating System is Active partition and it is the Primary partition. So we can call the active partition as Bootable Partition or Primary Partition.
(On Windows), the active partition is a primary partition on a disk which Windows will load its files from. An active partition is always a startup partition. If there are several OS's on the one disk, Windows will load from the one marked as active. - pentavore
system partition
System partition
Information for BIOS: the active partition is the partition from which an operating system (or another boot-loader) should be boot-loaded.
The boot partition
1.-schema partition 2.-configuration partition 3.-domain partition 4.-application partition
Active partition is a term Windows uses to mean the partition Windows will boot off of. The Windows boot loader goes to its configuration file and starts, these files will be in the active partition.
active partition
Must be at least a 2 GB partition. System partition.