GPT and MBR Disk Partition
Legacy Boot is the boot process used by BIOS firmware. The firmware maintains a list of installed storage devices that may be bootable (Floppy Disk Drives, Hard Disk Drives, Optical Disk Drives, Tape Drives, etc...) and enumerates them in a configurable order of priority. Once the POST procedure has completed, the firmware loads the first sector of each of the storage targets into memory and scans it for a valid Master Boot Record (MBR). If a valid MBR is found, the firmware passes execution to the boot loader code found in the MBR which allows the user to select a partition to boot from. If one is not found, it proceeds to the next device in the boot order.
MBR: Master Boot Record 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 organization of the partition table in the MBR limits the maximum addressable storage space of a disk to 2 TB (232 × 512 bytes). Therefore, the MBR-based partitioning scheme is in the process of being superseded by the GUID Partition Table (GPT) scheme in new computers. A GPT can coexist with an MBR in order to provide some limited form of backward compatibility for older systems.
UEFI boot is the boot process used by UEFI firmware. The firmware maintains a list of valid boot volumes called EFI Service Partitions. During the POST procedure the UEFI firmware scans all of the bootable storage devices that are connected to the system for a valid GUID Partition Table (GPT). Unlike a MBR, a GPT does not contain a boot loader. The firmware itself scans the GPTs to find an EFI Service Partition to boot from. If no EFI bootable partition is found, the firmware can fall back on the Legacy Boot method.
GPT: GUID Partition Table is a standard for the layout of the partition table on a physical hard disk, using globally unique identifiers (GUID). Although it forms a part of the Unified Extensible Firmware Interface (UEFI) standard (Unified EFI Forum proposed replacement for the PC BIOS), it is also used on some BIOS systems because of the limitations of master boot record (MBR) partition tables, which use 32 bits for storing logical block addresses (LBA) and size information.
MBR disk partition: Support the largest volume for 2 TB (Terabytes) and each disk supports one up to four primary partitions or three primary partitions, one extended partition and unlimited logical drive.
GPT disk partition: Support the maximum volume for 18 EB (Exabytes) and each disk partition has no upper limit, GPT disk partition is only limited by the operating system. Due to the partition table itself needs to occupy a certain space, so the space left for hard disk partition at the original plan determines the most partitions can have in disk. (From CCBoot v3.0 20140801, Server game disk support GPT disk partition.)
Details of GPT, please refer to http://en.wikipedia.org/wiki/GUID_Partition_Table.
Details of MBR, please refer to http://en.wikipedia.org/wiki/Master_boot_record.
Note : Usually UEFI (GPT) images have better boot time than Legacy (MBR).