Underclocking
Underclocking is the process of configuring a computer processor or other electronic circuit to operate at a lower speed than usual. This will reduce the speed of the computer, but it will usually make the battery last longer and the computer will produce less heat. Some computers automatically underclock themselves when the system is not doing a lot of work. For even further battery and heat savings a computer can be undervolted, where the processor is operated at a lower voltage than usual. Other devices such as video cards and smartphones can also be underclocked. The opposite of underclocking is called overclocking, and it is used to increase the speed of the computer but at the cost of battery life (if there is a battery) and heat output.