This document discusses open loop and closed loop control systems. An open loop system does not use feedback, so its output is not affected by its input and it cannot compensate for disturbances not accounted for in its design. A closed loop system uses feedback to minimize errors between its output and a desired setpoint, allowing it to reject disturbances and make the system more stable. Examples given of open loop systems are a clothes dryer controlled by a timer and closed loop systems include HVAC systems that use a thermostat for feedback control.