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GUID Partition Table

Computer data storage partitioning standard

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It has several advantages over master boot record (MBR) partition tables, such as support for more than four primary partitions and 64-bit rather than 32-bit logical block addresses (LBA) for blocks on a storage device. The larger LBA size supports larger disks.

Some BIOSes support GPT partition tables as well as MBR partition tables, in order to support larger disks than MBR partition tables can support.

GPT uses universally unique identifiers (UUIDs), which are also known as globally unique identifiers (GUIDs), to identify partitions and partition types.

All modern personal computer operating systems support GPT. Some, including macOS and Microsoft Windows on the x86 architecture, 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 either the BIOS or the EFI firmware interface.

History

The Master Boot Record (MBR) partitioning scheme, widely used since the early 1980s, had limitations when it came to modern hardware. The available size for block addresses and related information is limited to 32 bits. For hard disks with 512‑byte sectors, the MBR partition table entries allow a maximum size of 2 TiB (232 × 512‑bytes) or 2.20 TB (2.20 × 1012 bytes).

In the late 1990s, Intel developed a new partition table format as part of what eventually became the Unified Extensible Firmware Interface (UEFI). The GUID Partition Table is specified in chapter 5 of the UEFI 2.11 specification. GPT uses 64 bits for logical block addresses, allowing a maximum disk size of 264 sectors. For disks with 512‑byte sectors, the maximum size is 8 ZiB (264 × 512‑bytes) or 9.44 ZB (9.44 × 1021 bytes). For disks with 4,096‑byte sectors the maximum size is 64 ZiB (264 × 4,096‑bytes) or 75.6 ZB (75.6 × 1021 bytes).

In 2010, hard-disk manufacturers introduced drives with 4,096‑byte sectors (Advanced Format). For compatibility with legacy hardware and software, those drives include an emulation technology (512e) that presents 512‑byte sectors to the entity accessing the hard drive, despite their underlying 4,096‑byte physical sectors. Performance could be degraded on write operations, when the drive is forced to perform two read-modify-write operations to satisfy a single misaligned 4,096‑byte write operation. Since April 2014, enterprise-class drives without emulation technology (4K native) have been available on the market.

Readiness of the support for 4 KB logical sectors within operating systems differs among their types, vendors and versions. For example, Microsoft Windows supports 4K native drives since Windows 8 and Windows Server 2012 (both released in 2012) in UEFI.

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