Due to Microsoft limitation, the MBR (Main Boot Record) partition table is the default option for initializing hard disks. However, the MBR partition table can only manage up to a 2TB partition. For creating or using a partition bigger than 2TB, you must initialize the HDD as GPT (GUID Partition table) partition table format in the Disk management option of Administrative tools in the Windows control panel. This type of partition table can manage HDD size up to 18EB (1EB = 1024PB = 1048576TB), and allow up to 128 partitions.
GPT partition is implemented under Windows XP 64-bit, Windows Server 2003, Windows Vista, Windows Server 2008, Windows7, Windows Server 2008 R2 or later. For detailed information on GPT partition table, please refer to the following Microsoft FAQ: http://www.microsoft.com/whdc/device/storage/GPT_FAQ.mspx