Brake Calipers

Calipers are fixed to the frame of the bike (fork and/or swingarm) and are designed to grip the brake disc to stop the bike or deduce its speed.  Whilst the complete caliper is fixed to the bike, within itself the caliper can be of a floating or fixed type as described below.

Floating calipers move in and out relative to the rotor and have one or two pistons only on the inboard side of the rotor. This piston pushes the entire caliper when the brakes are applied, creating friction from the brake pads on both sides of the rotor.

Fixed calipers, as the name implies, don't move, but rather have pistons arranged on opposing sides of the rotor. Fixed calipers are generally preferred for their performance, but are more expensive than the floating kind. Some high-performance fixed calipers have two or more pairs of pistons (or "pots") arranged on each side of the rotor -- some have as many as six pairs total.

How the Floating or Sliding Caliper works
A caliper bracket is solidly mounted and the caliper itself within that bracket isn't solidly mounted so it can slide left and right via pins and bushings on the bracket.

A piston on the inner side of the disc pushes that brake pad as if to move the disc but because the disc can't slide, the force pulls the sliding caliper with another brake pad unto the other side of the disc.

The advantages of the floating caliper is that its cheaper and lighter than the fixed caliper as it uses less parts and is more compact.

How the Fixed Caliper works

The entire caliper is solidly mounted and there is a piston or pistons on both sides of the disc. The pistons push the two brake pads unto both sides of the disc.

The fixed cailper use multiple pistons sorted in pairs with two, four and six being the usual number of pistons as opposed to the one piston in the sliding type.

The fixed caliper can apply more squeezing power and apply that power more evenly during braking as force is directly applied to both sides even if its a two piston brake.

Fixed calipers also provide a better feel through the brake pedal whenever the driver applies the brake which is preferable for luxury and performance vehicles.

Both types of disc brakes are effective as part of an efficient braking system and this is evident by the fact that the less powerful floating caliper is used much more than the fixed caliper.

Another description

In contrast to a floating brake caliper, a fixed brake caliper doesn’t change its position with regard to the disc rotor once it is installed. The convergence of the brake pads towards the disc rotor only occurs through movement of the pistons. That is why the caliper pistons of fixed brake calipers have to always be arranged in opposite pairs. Fixed brake calipers are available with 2, 4, or 6 pistons.

A floating brake caliper can move sideways on a stator. This means you only have to include one (or several) caliper piston(s) on one side of the brake caliper. This then presses the brake pad to the disc rotor while simultaneously pulling the other brake pad to it. This “one-sidedness” is of advantage if there is no or only little space left on one side of the disc rotor which might be the case because a floating brake caliper is of very flat build on the side without caliper piston.

One of the (often overstated) disadvantages of a floating brake caliper is its proneness to making scraping noises. In general, because of its design, or more precise its higher degrees of freedom, it is harder to optimize a floating brake caliper than a fixed caliper. For instance, it is extremely difficult to achieve even contact pressure of the brake pads.

Sources: Why High End?, How Stuff Works, Engineering Explained, Trick St