Power may be conserved and battery life may be extended in a microprocessor controlled device by providing two microprocessors, one of which is a low power, low performance low speed processor for performing background tasks, the other of which is a high power, high performance, high speed processor for performing computationally intensive foreground tasks. The low speed processor activates the high speed processor when a high performance task is to be performed. When activating the high performance processor, the low performance processor also controls the device's power supply to provide high voltage to the high speed processor. The high speed processor may run at variable clock speeds, with power consumption of the processor increasing with increasing speed. The high speed processor selects its own clock speed based upon the task to be performed, by including a clock speed in each software subroutine which controls a task. The software subroutine associated with a task is thereby executed at its associated clock speed, which may be chosen to be the lowest possible clock speed consistent with the task to be performed.