A Device is a physical electronic resource with processing capability upon which Artifacts can be deployed for execution, as represented in a Deployment diagram. Complex Devices can consist of other devices; that is, a Device can be a nested element, where a physical machine is decomposed into its elements either through namespace ownership or through attributes that are typed by Devices.
OMG UML Specification
The OMG UML specification (UML Superstructure Specification, 10.3.7, v2.1.1, p. 207) states:
In the metamodel, a Device is a subclass of Node.