The most common handbrake layout used on a four-wheel disc brake system has a small auxiliary drum brake mounted inside the brake disc.
A pair of brake shoes, much the same as those in a normal rear drum brake, are moved outwards by the operation of the handbrake lever. They press against a 'drum' formed by the inner surface of the centre of the brake disc.
The shoes are fitted with a star wheel adjuster to compensate for wear. Once this adjuster has been used, the handbrake cable adjuster can be used to take up any remaining slack.