You’re wondering what makes a performance brake caliper so different from the one that your car came from the factory with. Your car’s brake system consists of the pedal, master cylinder, fluid and lines, and calipers and rotors at each wheel (or wheel cylinders and drums in the rear). When you push the brake pedal, the master cylinder forces fluid through the brake lines to each wheel. The brake fluid enters the caliper or wheel cylinder and expands a piston or pistons outward, applying force to the rotor or drum. Instead of one or two pistons per caliper, high performance calipers will have four, six or eight smaller pistons in them, which will multiply your braking force even more.
For more info, see Why a Big Brake Kit Won’t Make Your Car Stop Faster