The major components of the disc brake system are the brake pads, the caliper and the rotor (disc). The caliper is similar in function to the wheel cylinder used with drum brakes and the rotor is similar to the brake drum used in drum brakes.
The major difference between drum brakes and disc brakes is that with drum brakes, the wheel cylinder forces the brake shoes out against the brake drum to stop the vehicle, while with disc brakes, the caliper forces the brake pads inward to squeeze the rotor and stop the vehicle. The biggest advantage of disc brakes over drum brakes is that the caliper and brake pads enclose only a small portion of the rotor, leaving the rest of it exposed to outside air. This aids in rapid heat dissipation, reducing brake fade and it throws off water fast as well.