GUID Partition Table

GUID Partition Table (GPT) is a standard for the layout of the partition table on a physical storage device used in a desktop or server PC, such as a hard disk drive or solid-state drive, using globally unique identifiers (GUID). Although it forms a part of the Unified Extensible Firmware Interface (UEFI) standard (Unified EFI Forum proposed replacement for the PC BIOS), it is also used on some BIOS systems because of the limitations of master boot record (MBR) partition tables, which use 32 bits for storing logical block addresses (LBA) and size information on a traditionally 512 byte disk sector.

All modern PC operating systems support GPT. Some, including macOS and Microsoft Windows on x86, support booting from GPT partitions only on systems with EFI firmware, but FreeBSD and most Linux distributions can boot from GPT partitions on systems with both legacy BIOS firmware interface and EFI.

The widespread MBR partitioning scheme, dating from the early 1980s, imposed limitations that affect the use of modern hardware. One of the main limitations is the usage of 32 bits for storing block addresses and quantity information. For hard disks with 512-byte sectors, the MBR partition table entries allow up to a maximum of 2 TiB (2³² × 512 bytes).

Intel therefore developed a new partition table format in the late 1990s as part of what eventually became UEFI. As of 2010^[update], GPT forms a subset of the UEFI specification. GPT allocates 64 bits for logical block addresses, therefore allowing a maximum disk size of 2⁶⁴ sectors. For disks with 512-byte sectors, maximum size is 9.4 ZB (9.4 × 10²¹ bytes) or 8 ZiB (9,444,732,965,739,290,427,392 bytes, coming from 18,446,744,073,709,551,616 (2⁶⁴) sectors × 512 (2⁹) bytes per sector).

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