Most clutch release systems have either a semi-hydraulic or a fully hydraulic system. Originally a cable was used from the pedal to the clutch fork however as modern engine compartments are narrowing this method is no longer used.
SEMI-HYDRAULIC SYSTEMS
The clutch cable from the pedal to the clutch fork is replaced by a hydraulic line, master cylinder and slave cylinder. In this configuration the clutch fork is actuated by the slave cylinder.