Definition of a Function. A function is a relation for which each value from the set the first components of the ordered pairs is associated with exactly one value from the set of second components of the ordered pair. Okay, that is a mouth full.
Master cylinder without booster. Single bore master cylinders: These unboosted hydraulic Master Cylinders are actuated by foot effort, via the brake pedal. The brake pressure is related to actuation force and depends on the piston bore size: the smaller the bore, the higher the pressure.
The vacuum booster is attached between the master cylinder and the brake pedal and assists the braking force applied by the driver. These units consist of a hollow housing with a movable rubber diaphragm across the center, creating two chambers.