GPT (GUID Partition Table) is the preferred partitioning system for hard disks bigger than 2TB (the limit for MBR partitions). With GPT, you can define up to 128 partitions by default. Gaps can occur in partition numbering, so you can have a disk with partitions numbered 3, 12, and 99, for example.
GPT employs a protective MBR (the first sector of the disk), which is a legal MBR definition that makes GPT unaware programs think that the disk holds a single MBR spanning the entire disk. GPT supports disks of up to 8 ZB (Zettabytes), which is about 4 billion times larger then the MBR’s limit.