GUID Partition Table (GPT) is a standard for the layout of the partition table on a physical hard disk. It is a part of the Extensible Firmware Interface (EFI) standard proposed by Intel as a replacement for the outdated PC BIOS, one of the few remaining relics of the original IBM PC. The GPT replaces the Master Boot Record (MBR) used with BIOS. This article or section is in need of attention from an expert on the subject. ... In general, a partition is a splitting into parts. ... Typical hard drives of the mid-1990s. ... The workings of the Extensible Firmware Interface The Extensible Firmware Interface (EFI) is a software interface between an operating system and platform firmware. ... IBM PC (IBM 5150) with keyboard and green screen monochrome monitor (IBM 5151), running MS-DOS 5. ... BIOS, in computing, stands for Basic Input/Output System also incorrectly known as Basic Integrated Operating System. ... A master boot record (MBR) is the first sector (sector zero) of a data storage device such as a hard disk. ...

Features

Location and layout of the GUID Partition Table. Each LBA is 512 bytes.

While the MBR begins with the Master Boot Code, which contains executable binary for the purpose of identifying and booting the active partition, GPT relies on the extended capabilities of EFI for these processes. While an MBR entry begins the disk for protective and compatibility purposes, the GPT itself begins with the Partition Table Header. Image File history File links GUID_Partition_Table. ... Image File history File links GUID_Partition_Table. ... A Hexdump of a JPEG image. ... In computer engineering, hard disk drive partitioning is the creation of logical divisions upon a hard disk that allows one to apply operating system-specific logical formatting. ... The workings of the Extensible Firmware Interface The Extensible Firmware Interface (EFI) is a software interface between an operating system and platform firmware. ...

GPT uses modern logical block addressing (LBA) in place of the cylinder-head-sector (CHS) addressing used with MBR. Legacy MBR information is contained in LBA 0, the GPT header is in LBA 1, and the partition table itself follows. In 64-bit Windows operating systems, 16,384 bytes, or 32 sectors, are reserved for the GPT, leaving LBA 34 as the first usable sector on the disk. Logical block addressing in computing maps conceptual data storage onto secondary storage. ... Cylinder-head-sector, also known as CHS, is a method of addressing data on a hard drive. ... Microsoft Windows is the name of several families of proprietary operating systems by Microsoft. ... An operating system (OS) is a computer program that manages the hardware and software resources of a computer. ... A sector is a part of a whole. ...

GPT also provides for redundancy. The GPT header and partition table are written at both the beginning and end of the disk.

Legacy MBR (LBA 0)

The primary purpose of the MBR at the beginning of the disk is to prevent MBR-based disk utilities from mis-recognizing, and possibly over-writing, GPT disks. A single partition, encompassing the entire GPT drive, is indicated. The System ID for the partition is set to 0xEE, indicating that it uses GPT. Because of this, EFI ignores the MBR. Some 32-bit OSes which cannot read GPT disks nevertheless recognize this ID and present the disk as an inaccessible GPT disk.

Partition table header (LBA 1)

The partition table header defines the blocks on the disk that can be utilized by the user (the usable blocks). It also defines the number and size of the partition entries that make up the partition table. On 64-bit Windows Server 2003 machines, there are 128 partition entries reserved, each 128 bytes long. Thus, 128 partitions can be created.

The header contains the disk GUID (Globally Unique Identifier). It records its own size and location (always LBA 1) and the size and location of the secondary GPT header and table (always the last sectors on the disk). Importantly, it also contains a CRC32 checksum for itself and for the partition table, which is verified by EFI processes on boot. Because EFI uses and verifies this checksum, hex editors should not be used to modify the contents of the GPT. Such modification would render the checksum invalid. In this case, EFI would overwrite the primary GPT with the secondary one, or, if both GPTs contained invalid checksums, would be unable to access the disk. A Globally Unique Identifier or GUID is a pseudo-random number used in software applications. ...

Partition entries (LBA 2-33)

Partition entries are simple and straightforward. The first 16 bytes designate the partition type GUID. For example, the GUID for an EFI System partition is {28732AC1-1FF8-D211-BA4B-00A0C93EC93B}. The second 16 bytes contain a GUID unique to the partition. Starting and ending 64-bit LBAs are also recorded here, and space is allocated for partition names and attributes.

Partition type GUIDs

Note: Linux and Windows use the same GUID for their respective data partitions The EFI System Partition is a partition on a data storage device that is used by machines that adhere to the Extensible Firmware Interface. ... Microsoft Windows is the name of several families of proprietary operating systems by Microsoft. ... The Microsoft Reserved Partition is a partition on a data storage device that is used to reserve space ahead of time for other use[1]. It does not contain any meaningful data itself. ... This article or section may be confusing or unclear for some readers, and should be edited to rectify this. ... The Logical Disk Manager (LDM) is an implementation of a logical volume manager for Windows, developed by Microsoft and Veritas Software. ... HP-UX is Hewlett-Packards proprietary implementation of the Unix operating system. ... Linux refers to any Unix-like computer operating system which uses the Linux kernel. ... LVM is an implementation of a logical volume manager for the Linux kernel. ... FreeBSD is a Unix-like free operating system descended from AT&T UNIX via the Berkeley Software Distribution (BSD) branch through the 386BSD and 4. ... The UNIX file system (UFS) is a file system used by many Unix and Unix-like operating systems. ... Mac OS X (official IPA pronunciation: ) is a line of proprietary, graphical operating systems developed, marketed, and sold by Apple Inc. ... Hierarchical File System (HFS), is a file system developed by Apple Computer for use on computers running Mac OS. Originally designed for use on floppy and hard disks, it can also be found on read-only media such as CD-ROMs. ... Apple Inc. ... The UNIX file system (UFS) is a file system used by many Unix and Unix-like operating systems. ... Solaris is a computer operating system developed by Sun Microsystems. ...

Note: The GUIDs in this table are written assuming a little-endian byte order. For example, the GUID for an EFI System partition is written as C12A7328-F81F-11D2-BA4B-00A0C93EC93B here, which corresponds to the 16 byte sequence 28 73 2A C1 1F F8 D2 11 BA 4B 00 A0 C9 3E C9 3B. Note that only the first four blocks are byte-swapped. When integers or any other data are represented with multiple bytes, there is no unique way of ordering of those bytes in memory or in a transmission over some medium, and so the order is subject to arbitrary convention. ...

See also

• Master boot record
• GUID
• EFI
• Disk partitioning

A master boot record (MBR) is the first sector (sector zero) of a data storage device such as a hard disk. ... This article or section is in need of attention from an expert on the subject. ... The workings of the Extensible Firmware Interface The Extensible Firmware Interface (EFI) is a software interface between an operating system and platform firmware. ... In computer engineering, hard disk drive partitioning is the creation of logical divisions upon a hard disk that allows one to apply operating system-specific logical formatting. ...

External links

• Microsoft: Disk Sectors on GPT Disks
• Microsoft: Using GPT Drives on x86-64 Systems