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Protocols — Bootable Image Support
Version 1.10 12/01/02 11-9
Partition 1
Start partition
OM13160
PMBR
Partition
Table HDR
LBA0
LBA1
First useable block
Partition
Table HDR
Last useable block
LBAn
0 1 n
End partition
Primary Partition
Table
Backup Partition
Table
Start partition
End partition
0 1 n
Figure 11-2. GUID Partition Table (GPT) Scheme
The primary GUID Partition Entry array must be located after the primary GUID Partition Table
Header and end before the FirstUsableLBA. The backup GUID Partition Entry array must be
located after the LastUsableLBA and end before the backup GUID Partition Table Header.
Therefore the primary and backup GUID Partition Entry arrays are stored in separate locations on
the disk. GUID Partition Entries define a partition that is contained in a range that is within the
usable space declared by the GUID Partition Table Header. Zero or more GUID Partition Entries
may be in use in the GUID Partition Entry array. Each defined partition must not overlap with any
other defined partition. If all the fields of a GUID Partition Entry are zero, the entry is not in use.
A minimum of 16,384 bytes of space must be reserved for the GUID Partition Entry array.
Typically the first useable block will start at an LBA greater than or equal to 34, assuming the LBA
block size is 512 bytes.
Table 11-1. 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 range defined by
HeaderSize is “check-summed.”
Reserved 20 4 Must be zero.
continued