Question Croner...

What is the difference between disc brake and drum brake? How do they work?

A brake is used to apply frictional resistance to a moving machine member to retard the machine's motion. Early automotive systems used a drum design on all four wheels.
They were called drum brakes because the components were housed in a round drum that rotated along with the wheel. inside was a set of shoes that, when the brake pedal was pressed, would force the shoe against the drum and slow the wheel.
Fluid was used to transfer the movement of the brake pedal into the movement of the brake shoes, while the shoes themselves were made of heat-resistant friction material similar to that used on clutch plates.
This basic design had one major flaw. Under high braking conditions, like descending a steep hill with a heavy load or repeated high-speed slowdowns, drum brakes would often fade and lose effectiveness.
Usually this fading was the result of too much heat build-up within the drums. For this reason, drum brakes can only operate as long as they can absorb the heat generated by slowing a vehicle's wheel. Thought disc brakes rely on the same basic principles. Their design is far superior to that of drum brakes.
Disc brakes use a slim rotor and small caliper to halt wheel movement.
Within the caliper are two break pads, one on each side of the rotor, that clamp together when the brake pedal is pressed. Once again fluid is used to transfer the movement of the brake pedal into the movement of the brake pads.
But,unlike drum brakes, which allow heat to build up inside the drum during heavy braking, the rotor used in disc brakes is fully exposed. This exposure works to constantly cool the rotor, greatly reducing its tendency to overheat or cause fading.