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→Understanding GPT Disks
== Understanding GPT Disks ==
GPT disks differ quite considerably from MBR disks. GPT supports disks up to 18 Exabytes in size with up 128 partitions.
A GPT disk requires a number of special partitions....
At the start of a GPT disk is an MBR. The MBR in this case is provided purely so that the disk will be recognized by disk utilities that do not understand the GPT partition style. To an MBR disk utility, the disk will appear to be an MBR disk with a single partition taking up the entire disk space.
Immediately after the MBR is the primary GPT header which defines the blocks on the disk available for partitions and information about the number and respective sizes of the partitions on the disk. The GPT header also includes information about its own location on the disk drive and a pointer to a backup header located in the last sector of drive which is used in the event that the primary header becomes corrupted. Finally, the GPT header contains a CRC32 checksum of itself (including the partition table) so that the system firmware can verify the integrity of the information. If the checksum fails the firmware switches to the backup GPT header. If the checkum on backup GPT header fails the disk is unusable.
Each partition on a GPT disk has a header containing information about the partition type, the begin and end blocks of the partition and a unique partition GUID.
