The CPS (crank position sensor) is used in place of the sensor that used to be used in the distributor to inform the CPU or ECU of the position of the crankshaft, in order to determine when to fire the ignition coil.

On the older cars, the sensor in the distributor was also linked to a system of weights and springs as well as a vacuum diaphragm to incorporate changes in timing (advancing or retarding) based on engine speed (hence the centrifugal weights) and load (based on manifold vacuum). However, with the incorporation of the CPS, these determinations of appropriate advance/retard is determined by a "map" algorythm in the ECU -- it's all software, and the distributor is now empty of such pieces, and consists solely of the rotor, just to direct the secondary (high voltage) current to the respective sparkplug. In fact, you cannot adjust ignition timing anymore by rotating the distributor -- timing is entirely ECU controlled.

As for the knock sensor, it simply reacts to engine knock (it can be simulated by rapping a hammer against the engine's head) to signal the ECU to retard ignition timing. Knock can occur because of lower octane fuel, high temperatures, and a heavy load, or any combination of these factors. In fact, for your (our) cars, fuel that is an A.K.A. (formerly "(RON+MON)/2") of 91 is recommended to avoid having the car's timing retarded due to knock, which will reduce mileage and power output, although it will run adequately on fuel as low as 87 albeit with occasionally retarded timing (and lower mileage) as required by conditions.