Abstract: A computer system including a microprocessor and a circuit to provide a clock signal for the microprocessor is described. The circuit is responsive to a control signal for selecting a minimum clock signal frequency value and a maximum clock signal frequency value, with the maximum clock signal frequency value being adjusted in accordance with operating conditions of the central processor. Also the system includes a circuit which varies a magnitude of a supply voltage fed to the microprocessor in accordance with the temperature of the microprocessor and the operating frequency of the microprocessor. This arrangement provides an advantage to save power in computers. It is particularly advantageous for portable computers such as notebook computers to conserve battery charge, minimize heat dissipation in the microprocessor, and to minimize the size and weight of the battery used in the notebook for a given operating duration requirement.