BRAC-X Twin Port Brake System is designed as a floating caliper (also called a "sliding caliper") moves with respect to the disc; 2 pistons on one side of the disc pushes the inner brake pad until it makes contact with the braking surface, then pulls the caliper body with the outer brake pad so pressure is applied to both sides of the disc.
Floating caliper (double pistons) designs are subject to failure due to sticking which can occur due to dirt or corrosion if the vehicle is not operated regularly. This can cause the pad attached to the caliper to rub on the disc when the brake is released. This can reduce fuel effiency and cause excessive wear on the affected pad. Additional heat generated by the constantly rubbing pad can lead to warping of the disc also.
Brac-X Ventilated disc design helps to dissipate the generated heat and is commonly used on the more-heavily-loaded front discs.