File System Format
Version 1.02 12/12/00 311
Table 16-1. GUID Partition Table Header
Mnemonic
Byte
Offset
Byte
Length Description
Signature 0 8 Identifies EFI-compatible partition table header.
This value must contain the string “EFI PART”,
0x5452415020494645.
Revision 8 4 The specification revision number that this header
complies to. For version 1.0 of the specification
the correct value is 0x00010000.
HeaderSize 12 4 Size in bytes of the GUID Partition Table Header.
HeaderCRC32 16 4 CRC32 checksum for the GUID Partition Table
Header structure. The ranged defined by
HeaderSize is “check-summed”.
Reserved 20 4 Must be zero.
MyLBA 24 8 The LBA that contains this data structure.
AlternateLBA 32 8 LBA address of the alternate GUID Partition Table
Header.
FirstUsableLBA 40 8 The first usable logical block that may be
contained in a GUID Partition Entry.
LastUsableLBA 48 8 The last usable logical block that may be
contained in a GUID Partition Entry.
DiskGUID 56 16 GUID that can be used to uniquely identify the
disk.
PartitionEntryLBA 72 8 The starting LBA of the GUID Partition Entry array.
NumberOfPartitionEntries 80 4 The number of Partition Entries in the GUID
Partition Entry array.
SizeOfPartitionEntry 84 4 The size, in bytes, of each the GUID Partition
Entry structures in the GUID Partition Entry array.
Must be a multiple of 8.
PartitionEntryArrayCRC32 88 4 The CRC32 of the GUID Partition Entry array.
Starts at Partition Entry LBA and is
NumberOfPartitionEntries * SizeOfPartitionEntry in
byte length.
Reserved 92 BlockSize
– 92
The rest of the block is reserved by EFI and must
be zero.
The following test must be performed to determine if a GUID Partition Table is valid:
• Check the GUID Partition Table Signature
• Check the GUID Partition Table CRC
• Check that the MyLBA entry points to the LBA that contains the GUID Partition Table
• Check the CRC of the GUID Partition Entry Array
