Some basics of MBR v/s GPT and BIOS v/s UEFI
MBR
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 concept of MBRs was publicly introduced in 1983 with PC DOS 2.0.
The MBR holds the information on how the logical partitions, containing file systems, are organized on that medium. Besides that, the MBR also contains executable code to function as a loader for the installed operating system—usually by passing control over to the loader's second stage, or in conjunction with each partition's volume boot record (VBR). This MBR code is usually referred to as a boot loader.
The organization of the partition table in the MBR limits the maximum addressable storage space of a disk to 2 TB (232 × 512 bytes).[1] Therefore, the MBR-based partitioning scheme is in the process of being superseded by the GUID Partition Table (GPT) scheme in new computers.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 a backwards compatibility for older systems.
From http://en.wikipedia.org/wiki/Master_boot_record
GPT
GUID Partition Table (GPT) 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-based partition table schemes insert the partitioning information for (usually) four "primary" partitions in the master boot record (MBR) (which on a BIOS system is also the container for code that begins the process of booting the system). In a GPT, the first sector of the disk is reserved for a "protective MBR" such that booting a BIOS-based computer from a GPT disk is supported, but the boot loader and O/S must both be GPT-aware. Regardless of the sector size, the GPT header begins on the second logical block of the device.