On a disk with no partitions

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).