What is GPT disk?
GPT is short for GUID Partition Table, and it is one of architectures for partitioning disk drive to store data. Generally speaking, it was created to accommodate the larger partition sizes. Apart from size, GPT disks also provide more partitions to build.
What is MBR disk?
A Master Boot Record (MBR) is a special type of boot sector at the very beginning of partitioned computer mass storage devices like fixed disks or removable drives intended for use with IBM PC-compatible systems and beyond. The MBR holds the information on how the logical partitions, containing file systems, are organized on that medium. Besides that, the MBR contains executable code to function as an operating system-independent chain boot loader in conjunction with each partition's Volume Boot Record (VBR). What is wrong with MBR partitioning?
MBR disks support only four partition table entries, and MBR partitioning rules are complex and poorly specified. An MBR partition is identified by a two-byte field, and coordination is necessary to avoid collision. Today there is no single authoritative list of partition identifiers.
Why Do We Need GPT?
GPT disks can grow to a very large size. Theory speaking, one GPT disk can be up to 2^64 logical blocks, which are commonly sized in 512b, in length. Windows 95/98/ME, Windows NT4, Windows 2000, Windows 2003 32-bit, Windows XP 32-bit version have a limitation of 2TB per physical disk. Windows file systems currently are limited to 256 terabytes each. So at most you can create 128 partitions on GPT disk, but it is enough for all users.
Besides, the GPT disk partition format is well defined and fully self-identifying. Although GPT disks have those advantages, you can not make a disk both GPT and MBR. However, all GPT disks contain a Protective MBR.
GPT disk, a more advanced style, GPT partition style, is specially designed for the larger hard drive (disk capacity is larger than 2TB) while MBR disk is widely accepted nowadays. It is not easy to convert MBR GPT disk, due to it relates to the technical problems. However, AOMEI Partition Assistant Professional (PA Pro) enables you to realize convert GPT MBR disk without data loss.
Besides general description on gpt mbr disk, there are many articles related to disk mbr gpt: