GPT disk partition: data structures

GPT Disk Partitions.

Modern 64 bit PC’s don’t have legacy BIOS, they got EFI(Extensible Firmware Interface) instead! Systems with EFI use not only DOS partition system but also the GUID Partition Table (GPT). GPT disks are more reliable, support up to separate 128 partitions and use 64 bit LBA addressing.

GPT disk structure

A GPT disk consists of 5 areas:

  1. Protective MBR
  2. GPT Header
  3. Partition Table
  4. Partition Area
  5. Backup Area
GPT Disk scheme.

Protective MBR

Protective MBR starts in the very first sector of the GPT disk. It consists of a DOS partition table with only one partition entry defined in it. This partition type is 0xEE, occupies the entire disk and his purpose is to provide compability with legacy systems.

GPT Header

GPT Header starts in sector 1 of the GPT disk and contains the size and address of the partition table(up to 128 entries) and checksums of the header and the partition table, the starting and ending sectors of the Partition Area.

Partition table

Partition table consists of up to 128 partition entries. Each partition entry contains: start and end address of the current partition, attribute flags, partition type, name and 128 bit GUID.

Partition area

Partition area – a variety of sectors that would be allocated to partitions.

Backup Area

Backup area contains backup copies of the GPT Header and Partition table. It’s located straight after the Partition Area in the next following sector.

GPT Header data structure

Data structure for the GPT Header.

To be continued…

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