An indication of the vendor-specific hardware type of the
physical entity. Note that this is different from the
definition of MIB-II's sysObjectID.
An agent should set this object to an enterprise-specific
registration identifier value indicating the specific
equipment type in detail. The associated instance of
entPhysicalClass is used to indicate the general type of
hardware device.
If no vendor-specific registration identifier exists for
this physical entity, or the value is unknown by this agent,
then the value { 0 0 } is returned.