If you have several physical hard disks on your computer, you can mark a partition as active on each disk, but only the active partition on the first hard disk detected by your BIOS will start up the computer.
Trying to do otherwise will cause all kinds of problems.
You can only have one active partition per physical hard disk.
A logical drive or extended partition cannot be marked as active, only primary partitions can be changed to active.
Also, there are a few things to note about marking a partition as active: