A disc brake is the brake where there is a disc that is screwed into the wheel and the disc rotates as the wheel moves. as the brakes are applied the disc is caught and it stops rotating and simultaneously even the wheel stops rotating.  drum brakes use a wide cylinder that is open at the back, similar in apprearance to, well, a drum. the shaped curved shoes inside the drum moves outward rubbing against the interior of the drum causing the wheel to stop rotating as the brakes are applied. DISC BRAKES ARE BETTER THEN DRUM BRAKES.