Mountainbike disc brakes at good prices from starbike.com
Disc brakes feature smooth and massive brake power independent from nasty conditions like rain or mud. They're mainly found on mountain bikes, where much more brake power is needed than on road bikes.
The function principle of disc brakes differs completely from rim brakes. Instead of brake pads pushing on rim sidewalls, disc brakes push their brake pads on hub-mounted disc rotors. The brake pads sit inside a caliper, which is fixated with bolts on the fork/frame.
The disc brake rotors require a hub with a disc brake rotor mount. There are two: IS 2000 6-bolt, where the rotor is being fixated with 6 bolts, and Centerlock, a splined interface with a lockring similar to cassettes.
The advantages of disc brakes speak for themselves. The brake power is as smooth as high and blown inner tubes due to overheating rims caused by rim brake are no longer an issue. In addition the rotors are not an integral part of the wheel like the rim sidewalls used by rim brakes for braking.
The disadvantage of disc brake systems is their weight when compared to rim brakes.
Well known manufacturers of bicycle disc brakes are Avid, Magura or Shimano.