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