GUID Partition Table

Short for GUID Partition Table, GPT is a part of the EFI standard that defines the layout of the partition table on a hard drive. GPT is meant as a replacement to hard drives using a MBR partition table, which have a 2.20TB size limitation and extends upon UEFI. Using GPT a drive could support between 8 and 9.4 ZB depending on the sector size.

If you're using a version of Windows that supports GPT while setting up a drive in Disk Management you will receive a prompt similar to the below example. Selecting GPT and clicking Ok will initialize the disk as a GPT partition style.

The GUID Partition Table disk architecture was introduced as part of the Extensible Firmware Interface initiative. GUID Partition Table is a new disk architecture that expands on the older Master Boot Record (MBR) partitioning scheme that has been common to Intel-based computers.

A partition is a contiguous space of storage on a physical or logical disk that functions as though it were a physically separate disk. Partitions are visible to the system firmware and the installed operating systems. Access to a partition is controlled by the system firmware and the operating system that is currently active

GUID Partition Table disks can grow to a very large size. As of July 2001, the Microsoft implementation supports a hard disk of up to 18 EB (512 KB LBAs).

The number of partitions on a GUID Partition Table disk is not constrained by temporary schemes such as container partitions as defined by the MBR Extended Boot Record. The Microsoft implementation of GUID Partition Table is limited to 128 partitions. However, it is important to note that one partition is used for the EFI System Partition, one for the Microsoft Reserved and two more are used if you use dynamic disks. This leaves 124 partitions for data use.

The GUID Partition Table disk partition format is well defined and fully self-identifying. Data that is critical to the operating system is located in partitions and not in unpartitioned or "hidden" sectors. GUID Partition Table does not allow for hidden sectors or partitions. GUID Partition Table disks use primary and backup partition tables for redundancy and CRC32 fields for improved partition data structure integrity. The GUID Partition Table partition format uses version number and size fields for future expansion.

Each GUID Partition Table partition has a unique identification GUID and a partition content type, so no coordination is necessary to prevent partition identifier collision. Each GUID Partition Table partition has a 36-character Unicode name, which means that any software can present an easily readable name for the partition without any additional understanding of the partition.