The increasing importance of energy e ciency has produced a m ultitude of hardware devices with various power management features. This paper investigates memory controller policies for manipulating DRAM power states in cache-based systems. We d e v elop an analytic model that approximates the idle time of DRAM chips using an exponential distribution, and validate our model against trace-driven simulations. Our results show that, for our benchmarks, the simple policy of immediately

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... a DRAM chip to a lower power state when it becomes idle is superior to more sophisticated policies that try to predict DRAM chip idle time.