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.