GUID Partition Table

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GUID Partition Table is a new style of partitioning which is part of the UEFI Specification. It is different from the Master Boot Record (the more commonly used partitioning style) in many aspects and has many advantages.

For any partitioning style, the number of partitions that can be defined is based on the total space alloted for the partition table and the space required for storing the information of a single partition

What is Master Boot Record ?

The MBR partition table stores the partitions info as follows

440 bytes of the HDD - MBR boot code that is launced by the BIOS 441-446 bytes - MBR signature 447-510 bytes - 64 bytes - Information about primary partitions 511 and 512 bytes - MBR signature 0xAA55

The entire information about the primary partitions is limited to the 64 bytes alloted. To extend this, extended partitions were used. AN extended partition is simply a primary partition ( in the MBR ) which acts like a container for other partitions called logical partitions. So either one is limited to 4 primary partitions or 3 primary and 1 extende partitions with mnay logical partitions inside it.

Problems with MBR :-

1) Only 4 primary partitions or 3 primary + 1 extended partitions with many logical partitions inside it. If you have 3 primary + 1 extended partitions, and you have some free space outside the extended partition area, you cannot create a new partition over that space.

2) Within the extended partition, the logical partitions meta-data is stored in linked-list structure. So if one link is lost, all the logical partitions following that meta-data is lost.

3) MBR supports only 1 byte partition type codes which leads to many collisions.

4) MBR stores partition sector informations using 32-bit LBA values. This LBA length along with 512 byte sector size (more commonly used) limits the maximum addressable size of the disk to be 2 TB. Any space beyond 2 TB cannot be defined in a partition if MBR partitioning is used.

What is GUID Partition Table