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Extensible Firmware Interface Specification
8-16 12/01/02 Version 1.10
8.3.5 Media Device Path
This Device Path is used to describe the portion of the medium that is being abstracted by a boot
service. An example of Media Device Path would be defining which partition on a hard drive was
being used.
8.3.5.1 Hard Drive
The Hard Drive Media Device Path is used to represent a partition on a hard drive. The master boot
record (MBR) that resides in the first sector of the disk defines the partitions on a disk. Partitions
are addressed in EFI starting at LBA zero. Partitions are numbered one through n. A partition
number of zero can be used to represent the raw hard drive.
The MBR Type is stored in the Device Path to allow new MBR types to be added in the future.
The Hard Drive Device Path also contains a Disk Signature and a Disk Signature Type. The disk
signature is maintained by the OS and only used by EFI to partition Device Path nodes. The disk
signature enables the OS to find disks even after they have been physically moved in a system.
Table 8-24. Hard Drive Media Device Path
Mnemonic
Byte
Offset
Byte
Length
Description
Type 0 1 Type 4 – Media Device Path
Sub-Type 1 1 Sub-Type 1 – Hard Drive
Length 2 2 Length of this structure in bytes. Length is 42 bytes.
Partition Number 4 4 Partition Number of the hard drive. Partition numbers start
at one. Partition number zero represents the entire device.
Partitions are defined by entries in the master boot record in
the first sector of the hard disk device.
Partition Start 8 8 Starting LBA of the partition on the hard drive
Partition Size 16 8 Size of the partition in units of Logical Blocks
Partition Signature 24 16 Signature unique to this partition
MBR Type 40 1 MBR Type: (Unused values reserved)
0x01 – PC-AT compatible MBR. Partition Start and Partition
Size come from PartitionStartingLBA and
PartitionSizeInLBA for the partition.
0x02 – EFI Partition Table Header.
Signature Type 41 1 Type of Disk Signature: (Unused values reserved)
0x00 – No Disk Signature.
0x01 – 32-bit signature from address 0x1b8 of the type
0x01 MBR.
0x02 – GUID signature.