Controllers

A controller is any electrical component that is used to control an electrical or electro-mechanical subsystem. The primary benefit of a controller is dedicated electronics expressly designed for working with a particular technology. This offloads the primary system computer from directly managing the process. Controllers may be divided into two main categories: signal controllers and power controllers.
Signal controllers are dedicated to implementing one or more communication protocols. As an example, almost every CPU or AP has an integrated memory controller subsystem that manages the processor's interactions with the main memory. It handles many important functions such as queueing, thread access control, and address resolution, etc. so that the CPU's resources are not consumed. Some controllers are much simpler, such as the PWM controller, but still act to offload some amount of complexity. Controllers also contain specialized hardware to meet the electrical requirements of the communication protocol.
Power controllers are somewhat different because they are not necessarily as complex as signal controllers. However, they can manage the supply of large voltages or currents. A standard CPU would not be able to provide tens or hundreds or thousands of watts to a connected component. The power controller also does contain specialized hardware with high power ratings, such as power FETs and diodes, transformers, ferromagnetic core inductors, etc.