Energy conservation without performance degradation is an important goal for battery-operated computers, such as laptops and hand-held assistants. In this paper we determine the potential benefits of application-supported device management for optimizing energy and performance. In particular, we consider application transformations that increase device idle times and inform the operating system about the length of each upcoming period of idleness. We use modeling and experimentation to assess the potential energy and performance benefits of this type of application support for a laptop disk. Our main modeling results show that these benefits are significant. Our experimental results demonstrate that unless applications are transformed, they cannot accrue any of the predicted benefits. Overall, we find that the transformations can reduce disk energy consumption by as much as 89% with only a small degradation in performance.
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