Computers with an Intel Itanium processor use the Extensible Firmware Interface (EFI) between firmware, hardware, and OS. EFI has a new type of disk partitioning system, called the GUID (globally unique identifier) partition table (GPT). Unlike Master Boot Record (MBR) partitioned disks, data critical to platform operation is located in partitions instead of unpartitioned or hidden sectors. GPT partitioned disks have redundant primary and backup partition tables for improved partition data structure integrity.

Microsoft Support HowTo
HOW TO: Use the Diskpart.efi Utility to Create a GUID Partition Table Partition on a Raw Disk in Windows.

Transitioning to the Intel Itanium Architecture (PDF)
This paper reviews reasons to adopt Itanium microarchitecture, what the Itanium 2 processor provides, how to make the transition, and where the Intel Itanium-based solutions ecosystem can provide an advantage to the developer or end user.