The modern hydraulic brake system has two types: disc and drum brakes.
Disc brakes are usually on the front wheels. The disc plate or rotor turns
with the wheel. A caliper is used to hold two friction pads. When depressing
the brake pedal, the brake fuild under pressure forces piston in the caliper
to press the friction pads against the disc and slow down the car.
Drum brakes are used on the rear wheels. A brake drum turns with the
wheel. The drum contains the brake shoes with the attached lining friction
material. As the driver steps down the brake pedal, the brake fluid under
pressure forces the wheel cylinder pistons to move the shoes against the
inside surface of the drum, decelerating the car.
The parking brake system has a series of levers and cables. It is designed
to brake on either rear wheels or front wheels to park the car safely on
a hill. The parking brake system is independent of other hydraulic brakes.
It is also a back-up system for emergency brake.