Using GPT Drives

This article provides information about how GUID Partition Table (GPT) disks are used in the Microsoft Windows family of operating systems.

Introduction

A GPT disk uses the GUID partition table (GPT) disk partitioning system. A GPT disk offers these benefits:

• Allows up to 128 primary partitions. Master Boot Record (MBR) disks can support up to four primary partitions and an additional 124 partitions inside extended partitions.
• Allows a much larger partition size--greater than 2 terabytes (TB), which is the limit for MBR disks.
• Provides greater reliability because of replication and cyclical redundancy check (CRC) protection of the partition table.
• Can be used as a storage volume on all x64-based platforms, including platforms running Windows XP Professional x64 Edition. Starting with Windows Server 2003 SP1, GPT disks can also be used as a storage volume on x86-based Windows platforms.
• Can be used as a boot volume on x64-based editions of Windows 7, Windows Vista, and Windows Server 2008. Starting with Windows Server 2003 SP1, GPT disks can also be used as a boot volume on Itanium-based systems.

Note  Windows only supports booting from a GPT disk on systems that contain Unified Extensible Firmware Interface (UEFI) boot firmware.

For more information about GPT disks, refer to Windows and GPT FAQ.

GPT Format

Starting with Microsoft Windows 2000, the operating system uses the GPT format for the following types of disks:

• Basic disks are the storage types most often used with Windows. The term basic disk refers to a disk that contains partitions, such as primary partitions and extended partitions, and these in turn are usually formatted with a file system.
• Dynamic disks were first introduced with Windows 2000 and provide features that basic disks do not, such as the ability to create volumes that span multiple disks (spanned and striped volumes) and the ability to create fault-tolerant volumes (mirrored and RAID-5 volumes).

For more information about these disk types, refer to Basic and Dynamic Disks.

The GPT format used in basic and dynamic disks is illustrated in the following figure.

Figure 1. GPT Format

The protective Master Boot Record (MBR) area exists on a GPT partition table for backward compatibility with disk management utilities that operate on MBR. The GPT header defines the range of logical block addresses that are usable by partition entries. The GPT header also defines its location on the disk, its GUID, and a 32-bit cyclic redundancy check (CRC32) checksum that is used to verify the integrity of the GPT header. Each entry in the GUID partition table begins with a partition type GUID. The 16-byte partition type GUID, which is similar to a System ID in the partition table of an MBR disk, identifies the type of data that the partition contains and identifies how the partition is used, for example if it is a basic disk or a dynamic disk. Note that each GUID partition entry has a backup copy.

Creating GPT Drives

You can convert only empty, unpartitioned disks (raw drives or empty MBR drives) to the GPT format. To convert a volume that contains data, you must first manually delete the partition. You can use the following methods to create GPT disks:

• After you install a new raw disk, open the Disk Management console to start a wizard that you can use to configure the new disk. The wizard includes options to initialize the disk as MBR or GPT.
• Initialize the new disk later by using the Initialize Disk option in the Disk Management console.

Note  Starting with Windows Vista, you can install a Windows x64-based operating system on a GPT disk only if the computer has UEFI boot firmware installed. However, installing a Windows x64-based operating system on a GPT disk is not supported on Windows XP. Attempting to do so yields an error.

Converting GPT or MBR Drives

You can convert an existing partition format to another format. For more information, refer to the following TechNet articles:

• Change a Master Boot Record Disk into a GUID Partition Table Disk
• Change a GUID Partition Table Disk into a Master Boot Record Disk

Examining Drive Configurations

You can use the following methods to determine whether a drive is configured as a GPT or an MBR disk:

• In the Disk Management console, on the View menu, point to Top, and then click Disk List. The upper pane displays a list of disk drives that specifies the partition style in the last column.
• In the Disk Management console, right-click the drive to display conversion options:
  • If the drive is configured as an unpartitioned GPT disk, the Convert to MBR Disk option appears. If the drive is partitioned, this option is unavailable.
  • If the drive is configured as an unpartitioned MBR disk, the Convert to GPT Disk option appears. If the drive is partitioned, this option is unavailable.
• In the Disk Management console, right-click the driver, click Properties, and then click the Volume tab to display the partition style and other information.
• In Device Manager, right-click the drive and then on the Volume tab, click Populate to display the partition style and other information.
• Start the DiskPart utility and enter the command list disk. The disk list indicates GPT or MBR in the last column of the command output.

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