If the disk isn't partitioned, PARTITION needs to create the partition structure on the disk.
PARTITION ADD Dialogue
Partition standard (MBR or GUID) <GUID>:
Explanation - PARTITION prompts you for the type of partition scheme to use on the disk. The default scheme is shown in parentheses.
Response - Press Enter to select the default scheme, or enter MBR. Two partition schemes are supported by UOS. The older MBR scheme supports up to 4 partitions of up to 4,294,967,296 sectors each. On a disk with 512 byte sectors, this means that each partition can be up to 2 Terabytes in length. The newer GUID scheme allows for up to 128 partitions of up to 16 quintillion bytes each (for disks with 512 byte sectors).