GUID Partition Table (GPT) whitepaper

Introduction
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1. Introduction to GUID Partition Table (GPT)
1.1 What is a GPT disk?
The GUID Partition Table (GPT) was introduced as a part of the Extensible Firmware Interface
(EFI) initiative. GPT provides a more flexible mechanism for partitioning disks than the older
Master Boot Record (MBR) partitioning scheme that has been common to PCs.
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 before the system
boots the operating system, and then by the operating system after it starts.
1.2 Why do we need GPT?
MBR Extended Boot Records, the commonly used alternative to GPT, are constrained by
supporting only four primary partitions, by temporary schemes such as container partitions, and
by allowing volume size less than 2TB only. This inhibits their use in solutions that need more
primary partitions or larger volume size.
A superior disk partion format that is well defined and self identifying would address these
constraints while also allowing for greater reliability and better useability.
1.3 What’s a GPT Disk benefits?
A GPT disk uses the GUID partition table (GPT) disk partitioning system.
GPT disks can grow to a very large size. The number of partitions on a GPT disk is not
constrained by temporary schemes such as container partitions as defined by the MBR
Extended Boot Record (EBR).
The GPT disk partition format is well defined and fully self-identifying. Data critical to platform
operation is located in partitions and not in unpartitioned or "hidden" sectors. GPT disks use
primary and backup partition tables for redundancy and CRC32 fields for improved partition data
structure integrity. The GPT partition format uses version number and size fields for future
expansion.
Each GPT partition has a unique identification GUID and a partition content type, so no
coordination is necessary to prevent partition identifier collision. Each GPT partition has a 36-
character unicode name, which means that any software can present a human-readable name
for the partition without any additional understanding of the partition.
A GPT disk offers these benefits:
 Allows up to 128 primary partitions. (MBR disks can support up to four primary partitions
and an infinite number of partitions inside an extended partition.)
 Allows a much larger volume size - greater than 2 TB, which is the limit for MBR disks.