GUID Partition Table

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.

The Master Boot Record (MBR) partitioning scheme, widely used since the early 1980s, imposed limitations for use of modern hardware.

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).

[1] In the late 1990s, Intel developed a new partition table format as part of what eventually became the Unified Extensible Firmware Interface (UEFI).

[2]: 111  GPT uses 64 bits for logical block addresses, allowing a maximum disk size of 264 sectors.

[5][6] Readiness of the support for 4 KB logical sectors within operating systems differs among their types, vendors and versions.

The UEFI specification stipulates that a minimum of 16,384 bytes, regardless of sector size, are allocated for the Partition Entry Array.

[9] In operating systems that support GPT-based boot through BIOS services rather than EFI, the first sector may also still be used to store the first stage of the bootloader code, but modified to recognize GPT partitions.

The first 16 bytes of each entry designate the partition type's globally unique identifier (GUID).

Then follow the starting and ending 64 bit LBAs, partition attributes, and the 36 character (max.)

The layout of a disk with the GUID Partition Table. In this example, each logical block is 512 bytes in size and each entry has 128 bytes. The corresponding partition entries are assumed to be located in LBA 2–33. Negative LBA addresses indicate a position from the end of the volume, with −1 being the last addressable block.