How does a caliper work?
Today most cars have hydraulic disc brakes, on both front and back wheels. Their purpose is that the car can brake easy, quick and safe. Therefore, they are considered as a safety component.
This is also the reason why there are built up hydraulic circuts around the calipers. By this you make sure, that the car always brakes, even if a tube or a pipe breaks.
The brake system functions
When you step on the brake, cylinder and braking force amplifier fill the calipers with brake fluid through tubes and brake pipes. The pressure can reach 150 bar, when a catastrophic brake is made. When the fluid reaches the calipers, it pressures the piston against the brake and the friction between the rotating brake disc and the pads makes the car reduce the speed.