Disc brakes are also used on high performance bikes. The system is a mixed mechanical/hydraulic design, and perforations on the disc face help in the removal of water and brake cooling.

The disc is attached to the wheel hub carrier and the hydraulic pistons that push the brake pads onto the disc are attached to the bike frame.

The hydraulic actuator is connected to the hand controls and the high pressure brake fluid is distributed through the brake lines seen in the diagram. This type of system permits better modulation of the brake force and requires less adjustment than cable systems.

The application of hydraulic actuation is not restricted to disc brakes, and commercial systems for the cantilever style brakes are available.

From: http://amp-research.com