controller

A controller is a device or software component that directs the behavior of a system by processing input signals and generating output commands for actuators or other components.

Controllers can be hardware-based, such as microcontrollers and programmable logic controllers (PLCs), or software-based, as seen in applications that follow architectural patterns like model–view–controller (MVC).

In control engineering, controllers implement control algorithms that regulate a process. They rely on sensors to provide feedback and typically operate within a feedback loop to reach a desired setpoint while maintaining stability and performance.

Common control strategies include proportional–integral–derivative (PID) control, state-space methods, and adaptive or robust schemes. Practical implementations appear in industrial automation, robotics, automotive systems, and building management.

In software engineering, a controller handles user input, updates the model, and selects the view in the MVC pattern, acting as an interface between data and presentation.

In consumer electronics and gaming, a controller refers to a device that transmits user actions to a system, such as a gamepad, joystick, or touchscreen controller.

In networking and IT infrastructure, software controllers coordinate resources and policies, for example in software-defined networking or virtualization platforms. See also PID control, feedback, open-loop and closed-loop systems, and MVC architecture.