An exemplary microelectronic device is made up of two or more functional units, which are all disposed on a single chip, or die. The functional units on the die do not all need to be operational at a given time in the execution of a computer program that is controlling the microelectronic device. The present invention rapidly turns on and off the functional units of the microelectronic device as required by a program being executed. This power down can be achieved by turning off clock inputs to the functional units, interrupting the supply of power to the functional units, or deactivating input signals to the functional units. This results in a very significant reduction in power consumption and corresponding heat dissipation by the microelectronic device as compared to the conventional approach of keeping all functional units operational all of the time.