System Hierarchy

It is important to understand some key terms when we talk about systems, and their structure.

• system a complete and integrated set of procedures, processes, components and circuits that work together to achieve a specific purpose or function. Systems perform complex tasks or operations and often have input and output interfaces with the external environment
• subsystem groups of procedures, processes, components and circuits that work together to perform a function within a larger system
• circuit arrangement of components that perform a function within a system
• component basic building block used to create circuits, subsystems and systems

When you put this into a system that you know well, such as a toaster, the system itself is the whole product, the subsystems are the lever subsystem and the toasting sub-system, the circuit would be the toasting elements turned on and off by the switch, and a component would be the dial that is used to set the length of the toasting process.