What is the first step in the braking process described for disc brakes?

The braking process for disc brakes begins with pressure being transmitted to the caliper from the master cylinder. This step is crucial because the master cylinder generates hydraulic pressure when the driver applies the brake pedal. This hydraulic pressure is then sent to the calipers which house the pistons and brake pads.

Once the pressure reaches the caliper, it causes the pistons to move, which in turn pushes the brake pads against the rotor, creating friction that slows down the vehicle. Understanding this step is important, as it forms the foundation of how disc brakes operate, with the master cylinder acting as the control center that initiates the braking sequence.

The other options involve stages that occur after pressure has already been established in the caliper and do not represent the initial action that starts the braking process.