Device Path Protocol
Version 1.02 12/12/00 119
5.3 Device Path Nodes
There are six major types of Device Path nodes:
Hardware Device Path. This Device Path defines how a device is attached to the resource
domain of a system, where resource domain is simply the shared memory, memory mapped
I/O, and I/O space of the system.
ACPI Device Path. This Device Path is used to describe devices whose enumeration is not
described in an industry-standard fashion. These devices must be described using ACPI
AML in the ACPI name space; this Device Path is a linkage to the ACPI name space.
Messaging Device Path. This Device Path is used to describe the connection of devices
outside the resource domain of the system. This Device Path can describe physical
messaging information (e.g., a SCSI ID) or abstract information (e.g., networking protocol
IP addresses).
Media Device Path. This Device Path is used to describe the portion of a medium that is
being abstracted by a boot service. For example, a Media Device Path could define which
partition on a hard drive was being used.
BIOS Boot Specification Device Path. This Device Path is used to point to boot legacy
operating systems; it is based on the BIOS Boot Specification Version 1.01.
End of Hardware Device Path. Depending on the Sub-Type, this Device Path node is used
to indicate the end of the Device Path instance or Device Path structure.

5.3.1 Generic Device Path Structures

A Device Path is a variable-length binary structure that is made up of variable-length generic
Device Path nodes. Table 5-1 defines the structure of a such a node and the lengths of its
components. The table defines the type and sub-type values corresponding to the Device Paths
described Section 5.3; all other type and sub-type values are Reserved.
Table 5-1. Generic Device Path Node Structure
Mnemonic
Byte
Offset
Byte
Length Description
Type 0 1 Type 0x01 – Hardware Device Path
Type 0x02 – ACPI Device Path
Type 0x03 – Messaging Device Path
Type 0x04 – Media Device Path
Type 0x05 – BIOS Boot Specification Device Path
Type 0xFF – End of Hardware Device Path
Sub-Type 1 1 Sub-Type – Varies by Type. (See Table 5-2.)
Length 2 2 Length of this structure in bytes. Length is 4 + n bytes.
Specific Device Path Data 4 nSpecific Device Path data. Type and Sub-Type define
type of data. Size of data is included in Length.