A heat sink is a component designed to dissipate heat from a CPU or GPU to prevent overheating; it does this by conducting heat away from the processor and towards fins where it is dissipated into the surrounding air. Thermal paste, in contrast, is used to optimize heat transfer between the CPU and the heat sink but does not itself dissipate heat. A fan helps blow hot air away but is most effective when used in conjunction with a heat sink. Liquid is a medium used in liquid cooling systems but is not itself a component that directly conducts heat away.