Intel Extensible Firmware Interface, Specification

Page: 331 / 494

File System Format
Version 1.02 12/12/00 313
The SizeOfPartitionEntry variable in the GUID Partition Table Header defines the size of a GUID
Partition Entry. The GUID Partition Entry starts in the first byte of the GUID Partition Entry and
any unused space at the end of the defined partition entry is reserved space and must be set to zero.
Each partition record contains a Unique Partition GUID variable that uniquely identifies every
partition that will ever be created. Any time a new partition record is created a new GUID must be
generated for that partition, and every partition is guaranteed to have a unique GUID. The partition
record also contains 64-bit logical block addresses for the starting and ending block of the partition.
The partition is defined as all the logical blocks inclusive of the starting and ending usable LBA
defined in the GUID Partition Table Header. The partition record contains a partition type GUID
that identifies the contents of the partition. This GUID is similar to the OS type field in the legacy
MBR. Each file system must publish its unique GUID. The partition record also contains
Attributes that can be used by utilities to make broad inferences about the usage of a partition. A
36 character Unicode string is also included, so that a human readable string can be used to
represent what information is stored on the partition. This allows third party utilities to give human
readable names to partitions.
The firmware must add the PartitionTypeGuid to the handle of every active GPT partition using
InstallProtocolInterface()
. This will allow drivers and applications, including OS
loaders, to easily search for handles that represent EFI System Partitions or vendor specific
partition types.
A utility that makes a binary copy of a disk that is formatted with GPT must generate a new
DiskGUID in the Partition Table Headers. In addition, new UniquePartitionGuids must be
generated for each GUID Partition Entry.
Table 16-3. Defined GUID Partition Entry - Partition Type GUIDs
Description GUID Value
Unused Entry 00000000-0000-0000-0000-000000000000
EFI System Partition C12A7328-F81F-11d2-BA4B-00A0C93EC93B
Partition containing a legacy MBR 024DEE41-33E7-11d3-9D69-0008C781F39F
OS vendors need to generate their own GUIDs to identify their partition types.
Table 16-4. Defined GUID Partition Entry - Attributes
Bits Description
Bit 0 Required for the platform to function. The system can not function normally if this partition is
removed. This partition should be considered as part of the hardware of the system, and if it is
removed the system may not boot. It may contain diagnostics, recovery tools, or other code or
data that is critical to the functioning of a system independent of any OS.
Bits1-47 Undefined and must be zero. Reserved for expansion by future versions of the EFI
specification.
Bits 48-63 Reserved for GUID specific use. The use of these bits will vary depending on the
PartitionTypeGuid. Only the owner of the PartitionTypeGuid is allowed to modify these bits.
They must be preserved if Bits 0-47 are modified.