How do wedge brakes differ from S-cam brakes in their operation?

1. Wedge brakes use a wedge pushed between the brake shoes by the push rod, while S-cam brakes use a rotating S-shaped cam
2. Wedge brakes are only used on the front axle, while S-cam brakes are only used on the rear
3. Wedge brakes use hydraulic fluid, while S-cam brakes use compressed air
4. There is no functional difference; they are just different names for the same system