Intel Extensible Firmware Interface, Specification

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Extensible Firmware Interface Specification
310 12/12/00 Version 1.02
Partition Entry array is the PartitionEntrySize multiplied by NumberOfPartitionEntries. When a
GUID Partition Entry is updated the PartitionEntryArrayCRC must be updated. When the
PartitionEntryArrayCRC is updated the GUID Partition Table Header CRC must also be updated,
since the PartitionEntryArrayCRC is stored in the GUID Partition Table Header.
Parti
tion
Table HDR
Partition 1
PMBR Parti
tion
Table HDR
0 1 n
...
LBA0 LBA1
LBAn
Start partition
End partition Start partition
Primary Partition
Table
Backup Partition
Table
0 1 n
...
End partition
First useable block
Last useable block
OM10322
Figure 16-2. 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.