Also known as ABS (and some people say ABS braking, which is as bad as saying
ATM machine), Anti-lock Braking Systems allow a
vehicle to reduce it's speed with far better
control than with
conventional brakes.
The theory is that, when rapidly braking, the more traction you have, the more control you have because the tyres are actually still turning and not sliding on the road surface.
ABS brakes actually consist of four main components. The speed sensors, the pump, a controller and valves.
All four work together to slow the wheel as fast as possible without allowing it to lock.
The controller is the system that keeps an eye on the speed sensors and controls the valves. It's a small computer sitting in the car itself.
The sensors purely monitor the speed on the wheel, passing acceleration or deceleration data to the controller.
The valves sit in three stages; open, which allows brake pressure to increase, closed, which stops more pressure and maintains an equal pressure on the brake and release, which allows pressure to decrease to the brake.
The pump is what increases the pressure on the brake lines.
While applying ABS brakes, you may feel the pedal pulse in and out. This is the controller increasing and decreasing pressure on the brake itself to keep the decelerating wheel at maximum slowing power without locking.
As a safety tip, when driving a car with ABS, don't pump the pedal. If you need to stop in an emergency hit the brake as firmly as possible and let it pulse like crazy and do all the work. This let's you concentrate more on actually steering to avoid that idiot in the 4 wheel drive that just cut you off.