The Ultimate design is cross-drilled and slotted.   In order to perform well and last, it is important for brake rotors or brake disc to keep cool.  Cross-drills and slots help to create additional pathways for heat to escape, gradually cooling down your brake discs and enhancing stopping performance as well as preventing your rotors from warping or cracking.  Slots or lined grooves that are machined just below the surface of the brake rotor create grip and help clear away debris from the friction surface.  They also help to maximize the contact between the brake pads and brake rotors, which boosts stopping ability.