The format used to define the hard disk partitions in computers with UEFI startup firmware. The GUID Partition Table (GPT) replaces the previous master boot record (MBR). GPT partitions can hold 18 exabytes compared to 2.2TB for the MBR. GPT supports a "protective" MBR so that third-party MBR utilities can identify the disk correctly, as well as a "legacy" MBR if the first partition must boot as an MBR drive. See
UEFI and
MBR disk.