There are two types of calipers used in performance applications. The first is a "fixed caliper" configuration. With the typical fixed caliper configuration, the caliper houses 2 to 4 pistons that squeeze the brake pads on both sides of the rotor. The caliper is bolted to the steering knuckle. It is fixed in position and does not move. All the motion needed to squeeze the pads occurs when the pistons move. The second type is a "floating caliper" system. In a typical floating caliper system, a single piston pushes against the inner brake pad. The caliper can float (slide) a short distance on guide pins, allowing it to force the outer brake pad against the rotor. A bracket supports the guide pins, and bolts to the steering knuckle.
Most passenger cars use floating calipers while many performance cars use fixed calipers. Most floating caliper brakes only have one piston. This allows the floating caliper setup to be less expensive and lighter. It works well for passenger car applications. The fixed calipers provide a smoother and stronger braking, improving both brake feel and stopping power. Fixed calipers may use from 1 to 4 pistons on each side of the caliper, or 2 to 8 in total. This has performance benefits, but the fixed calipers are heavier, take up more space, and are more complex to maintain due to the additional pistons.