What two features do most modern control systems share?

Most modern control systems share two fundamental characteristics:

• Power-driven actuation: The value of the controlled quantity is adjusted by a motor (in a generalized sense) that draws power from a local source rather than from the incoming signal itself. This ensures that a large amount of power is available to effect changes without loading or distorting the signals upon which the system's accuracy depends.1
• Feedback-based regulation: The rate at which energy is supplied to the motor to adjust the controlled quantity is determined by a function of the difference between the actual and desired values of that quantity. This mechanism allows the system to correct its operation based on real-time feedback.1

Systems possessing these two features are classified as closed-loop control systems or servomechanisms.1