The Input class is derived from the Port class and is used to simulate an input port of a component. The input ports of a component are all stored in the I_List public member of the Component class and can therefore be accessed by outside objects as is the case in the real world. The primary purpose of an Input object is to permit the enclosing component to receive signals from the external feeding connectors in the hierarchy immediately above the port. The Input object is also responsible for notifying all the subcomponents which it feeds to process their inputs.