The partition that contains the boot files for the operating system you want to run, that is, the partition from which the computer starts up. On a computer running Microsoft Windows 2000 or Windows NT that is based on the x86 family of CPUs (an x86-based computer), the active partition must be a primary partition. In addition, on a computer running Windows 2000, the active partition must be on a basic disk.
Alpha-based computers have no active partitions; these are configured by the manufacturer-supplied configuration program.
Depending on your platform, you can use any of the following tools to make a partition active: