Short for GUID Partition Table
, GPT was introduced as part of the Unified Extensible Firmware Interface (UEFI) initiative. GPT provides a more flexible mechanism for partitioning disks than the older Master Boot Record (MBR) partitioning scheme that was common to PCs. For instance, the hard drive using GPT partition framework can support volume as large as 18 EB (MBR only supports volume within 2TB), and the GPT doesn't limit partition quantity (MBR supports at most four primary partitions).
A partition is a contiguous space of storage on a physical or logical disk that functions as if 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 is started.