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GUID Partition Table

Created: 06.10.2020

GUID is an identifier of the following format: 8-4-4-4-12. There is still a protective MBR at 0 so that Windows will not try to format the disk. Up to 128 partitions, each entry is 128 bytes long -> . The header is located in sector 1. Backup copy at the end of the disk. Uses GUID as partition identifiers.


Up to a 128 partitions, all of them can be set as bootable. Will still have a dummy MBR at sector 0 and it’s there for backwards compatibility.


  • Protective MBR record. At the offset where there are normally partiton entries, there is just one entry of type 0xEE, which starts at sector 1 and is 0xFFFFFF sectors large. This is the pointer to the GPT header.
  • 0x00 offset. ASCII - EFI PART (0x45 46 49 20 50 41 52 54). This is a GPT signature.
  • 0x20 offset. LBA of backup copy.
  • 0x28. LBA start of partition area (⚠️ in sectors!!!).
  • 0x30. LBA end of partition area (⚠️ in sectors!!!).
  • 0x38. Disk GUID.
  • 0x48. LBA start of partition tables.


A GPT entry contains:

  • 0x00. Partition type GUID. Partition type GUIDs are listed on the Wikipedia page [2].
  • 0x10. Partition GUID.
  • 0x20. Start LBA
  • 0x28. End LBA
  • 0x30. Partition flags (read only, hidden flags etc)
  • 0x38. Partition name in Unicode.

Below is the live example of an entry:


⚠️ Remember that all the values are little-endian!


[1] InfoSec Institute Course, Coursera (all pictures are from the course or from the lab that I followed when watching the course). Definitely the one worth buying. Believe me.

[2] GPT, Wikipedia