Master Boot Record (MBR) and Globally Unique Identifier Partition Table (GPT) are two different disk-partitioning systems. MBR is the most common system and is supported by every version of Windows, including Windows Vista and Windows 7. GPT is an updated and improved partitioning system and is supported on Windows Vista, Windows 7, Windows Server 2008, and 64-bit versions of Windows XP and Windows Server 2003 operating systems.

GPT offers several advantages over MBR:

• In Windows, GPT can support up to 128 partitions. MBR supports only four partitions.
• GPT accurately describes physical disk geometry, allowing Windows to create partitions and logical drives on cylinder boundaries. Although Windows attempts to do this for MBR, the geometry that MBR reports has no relationship to a modern drive's physical geometry because it has been altered to enable larger capacities. Different disk vendors have created vendor-specific workarounds for this problem that are difficult to manage. Therefore, partitioning is more reliable when using GPT.
• GPT can support larger partition sizes. In theory, a GPT disk can be up to 18 exabytes in size (about 18,000,000 terabytes).
• GPT uses primary and backup partition tables for redundancy and CRC32 fields for improved partition data structure integrity. MBR does not have redundant partition tables.