GUID Partition Table (GPT)
GPT is the latest standard for laying out the partitions of a hard disk. It makes use of globally unique identifiers (GUID) to define the partition and it is part of the UEFI standard. This means that on a UEFI-based system (which is required for Windows 8 Secure Boot feature), it is a must to use GPT. With GPT, you can create theoretically unlimited partitions on the hard disk, even though it is generally restricted to 128 partitions by most OSes. Unlike MBR that limits each partition to only 2TB in size, each partition in GPT can hold up to 2^64 blocks in length (as it is using 64-bit), which is equivalent to 9.44ZB for a 512-byte block (1 ZB is 1 billion terabytes). I
n Microsoft Windows, that size is limited to 256TB.
There is a primary GPT at the beginning of the hard disk and a secondary GPT at the end. This is what makes GPT more useful than MBR. GPT stores a backup header and partition table at the end of the disk so it can be recovered if the primary tables are corrupted. It also carry out CRC32 checksums to detect errors and corruption of the header and partition table.
There is a protective MBR at the first sector of the hard disk. Such hybrid setup is to allow a BIOS-based system to boot from a GPT disk using a boot loader stored in the protective MBR’s code area. In addition, it protects the GPT disk from damage by GPT-unaware disk utilities.
Intel Macs are using GPT by default and you won’t be able to install Mac OS X (without tweaks and hacks) on a MBR system. Mac OS X will run on MBR disk though, it is just that you won’t be able to install on it.
Most Linux kernels come with support for GPT. Unless you are compiling your own kernel and you didn’t add this feature in, you should have no problem getting your favorite distro to work in GPT disk. One thing to note, you will have to use Grub 2 as the bootloader.
For Windows, only the 64-bit version of Windows from XP onward support booting from GPT disk. If you are getting a laptop pre-installed with 64-bit Windows 8, most probably it is using GPT. For Windows 7 and earlier version, the default configuration will be MBR instead of GPT
MBR was first introduced with IBM PC DOS 2.0 in 1983. It’s called Master Boot Record because the MBR is a special boot sector located at the beginning of a drive. This sector contains a boot loader for the installed operating system and information about the drive’s logical partitions. The boot loader is a small bit of code that generally loads the larger boot loader from another partition on a drive. If you have Windows installed, the initial bits of the Windows boot loader reside here—that’s why you may have to repair your MBR if it’s overwritten and Windows won’t start. If you have Linux installed, the GRUB boot loader will typically be located in the MBR.