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Extensible Firmware Interface Specification
11-12 12/01/02 Version 1.10
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 11-3. 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 11-4. Defined GUID Partition Entry - Attributes
Bits Description
Bit 0 Required for the platform to function. The system cannot 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.
11.2.2.2 ISO-9660 and El Torito
IS0-9660 is the industry standard low level format used on CD-ROM and DVD-ROM. CD-ROM
format is completely described by the “El Torito” Bootable CD-ROM Format Specification
Version 1.0. To boot from a CD-ROM or DVD-ROM in the boot services environment, an EFI
System partition is stored in a “no emulation” mode as defined by the “El Torito” specification. A
Platform ID of 0xEF hex indicates an EFI System Partition. The Platform ID is in either the
Section Header Entry or the Validation Entry of the Booting Catalog as defined by the “El Torito”
specification. EFI differs from “El Torito” “no emulation” mode in that it does not load the “no
emulation” image into memory and jump to it. EFI interprets the “no emulation” image as an EFI
system partition. EFI interprets the Sector Count in the Initial/Default Entry or the Section Header
Entry to be the size of the EFI system partition. If the value of Sector Count is set to 0 or 1, EFI
will assume the system partition consumes the space from the beginning of the “no emulation”
image to the end of the CD-ROM.