Power Steering relates to Power Assisted Steering. When you turn the steering wheel of your motor vehicle; sensors detect thhe change in postion and an hydraulic pump or servo motor provides additional power to help turn the wheels in the desired direction
Most cars use a hydraulic system. The engine drives an hydraulic pump via a belt or drivechain that pressurises the hydraulic steering system.
Hydraulic steering systems often fail when the drive belt snaps or a leak develops and hydraulic steering fluid leaks and pressure is lost.
Electrical Servo Motors are also becoming popular. A position sensor on the steering wheel sends information to a mini computer that controls the servo. Any change in position is converted into a signal that sends power to the servo. A mechanical steering linkage is also present in case of system failure.