On basic disks, marks the partition with focus as active. Only partitions can be marked as active. A partition must be selected for this operation to succeed. Use the select partition command to select a partition and shift the focus to it.
DiskPart only informs the basic input/output system (BIOS) or Extensible Firmware Interface (EFI) that the partition or volume is a valid system partition or system volume, and is capable of containing the operating system startup files. DiskPart does not check the contents of the partition. If you mistakenly mark a partition as active and it does not contain the operating system startup files, your computer might not start.
To mark the partition with focus as the active partition, type: