A data processing system includes a power supply, a plurality of processors wherein each processor is separately powerable by the power supply under operating system control. The operating system determines periodically a measure of system utilization and controls the switches to alter the number of active (powered) processors where the number of active processors reflects the measured system utilization and a set of utilization threshold values. System utilization may be based on the number of active tasks. The utilization thresholds preferably include a maximum threshold and a minimum threshold. A measured utilization exceeding the maximum threshold causes an increase in the number of active processors while utilization less than the minimum threshold causes a decrease in the number of active processors. The utilization thresholds may be determined from threshold factors that reflect time and date information, quality of service information, or a weighted average of historical utilization values.