Intel Extensible Firmware Interface - Manual (Page 862)

Extensible Firmware Interface Specification
C-6 12/01/02 Version 1.10
C.5 ACPI Terms
Names in the ACPI name space that start with an underscore (“_”) are reserved by the ACPI
specification and have architectural meaning. All ACPI names in the name space are four
characters in length. The following four ACPI names are used in this specification.
_ADR. The Address on a bus that has standard enumeration. An example would be PCI, where
the enumeration method is described in the PCI Local Bus specification.
_CRS. The current resource setting of a device. A _CRS is required for devices that are not
enumerated in a standard fashion. _CRS is how ACPI converts nonstandard devices into Plug and
Play devices.
_HID. Represents a device’s Plug and Play hardware ID, stored as a 32-bit compressed EISA ID.
_HID objects are optional in ACPI. However, a _HID object must be used to describe any device
that will be enumerated by the ACPI driver in the OS. This is how ACPI deals with non–Plug and
Play devices.
_UID. Is a serial number style ID that does not change across reboots. If a system contains more
than one device that reports the same _HID, each device must have a unique _UID. The _UID only
needs to be unique for device that have the exact same _HID value.