Geyser-1, a prototype MIPS R3000 CPU with fine grain runtime PG for major computational components in the execution stage is available. Function units such as CLU, shifter, multiplier and divider are power-gated and controlled at runtime such that only the function unit to be used is powered-on to minimize the leakage power. The evaluation results on the real chip reveals that the fine grain runtime PG mechanism works without electric problems. It reduces the leakage power 7% at 25 °C and 24% at 80°C. The evaluation results using benchmark programs show that the power consumption can be reduced from 3% at 25°C and 30% at 80° C.