Intel RC6 - Intel's Graphics Render C-State 6.
Render C-State (RC6) is a technique designed to optimize the average power to the graphics render engine during times of idleness of the render engine. RC6 is entered when the graphics render engine, blitter engine and the video engine have no workload being currently worked on and no outstanding graphics memory transactions. When the render engine idleness condition is met: The graphics VR will lower the graphics voltage rail (VAXG) into a lower voltage state (0.3 V).The render frequency clock will shut down.
Intel® Core™ i7-600, i5-500, i5-400 and i3-300 Mobile Processor Series Datasheet — Volume One, п. 4.6.2