====== Ubuntu - Boot - GUID Partition Table (GPT) ======

Globally Unique Identifier Partition Table (GPT).

The [[[[Ubuntu:Boot:Master Boot Record (MBR)|Master Boot Record (MBR)]] type partition table keeps information such as the four primary partition in the first 512 bytes of the hard disk.  In case of GPT the first sector is kept for "protective MBR" so that, old bios based computers can also boot from GPT partition table.

The GPT partition information starts from the second block (called LBA 1).

<WRAP notice>
**NOTE**: LBA is nothing but the sectors numbered in such a way that it can be easily addressed, where LBA 0 is for MBR, LBA 1 for GPT header info etc.
</WRAP>

Most of the time LBA 2 contains the GPT partition array entry.

The partition array entry typically reserves 128 bytes for each partition entry.  For a disk of 512-byte sectors the partition array entry can reach up to 16,384 bytes.  And in most cases the 34'th sector (or block) is the first usable sector in the disk.

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===== Merits of GPT partitioning =====

  * GPT supports up to 128 partitions so there is no need for extended of logical partitions.
  * GPT addresses use a 64-bit number LBA scheme, so it can address up to 8 ZiB size partitions.
  * GPT structure has primary and secondary headers, so recovery is more promising that MBR
  * GPT provides 1-byte partition code, but GPT give you a 16-byte GUID value to uniquely identify the partition.

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===== Tools for Creating GPT partitions =====

**fdisk** cannot create a GPT partition so we need to use some other tool to create it.

  * **Parted** can be used to create a GPT partition table, and partitions of more than 2TB size.
  * **Gdisk** is also a nice graphical tool to create a GPT partition table.

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===== Alternatives =====

See [[Ubuntu:Boot:Master Boot Record (MBR)|Master Boot Record (MBR)]].