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Smartphone consumers, app developers, and even mobile systems researchers operate under the assumption that performance differences between identical smartphones should be small. Consumers pick a model to purchase and don't consider that the specific device they leave the store with may vary quite dramatically from the identical models it sat next to on the shelf. App rating systems typically collect the model from reviewers, but not more detailed informationagain, assuming that all instances of a particular model perform similarly. Even mobile systems researchers will conduct studies using small numbers of devices that fail to account or control for inherent differences between identical phones. Unfortunately seemingly-identical smartphones can in fact have very different performance characteristics. Note that we are not referring to differences in battery or Flash performance caused over time by wear. Inherent differences would separate two brand-new phones still in the original packaging. Our experiments show up to 20% performance and energy consumption differences between otherwise identical devices. These differences result from process variation in the manufacture of smartphone CPUs, which causes some CPUs to perform much more poorly than others. This paper explains the causes of this variation, measures its impacts, and discusses implications for smartphone researchers, software developers, and consumers.

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As the rapid pace of smartphone improvements drives consumer appetites for the latest and greatest devices, the hidden cost is millions of tons of e-waste containing hazardous chemicals that are difficult to dispose of safely. Studies show that smartphone users are replacing their devices every 18 months, almost three times faster than desktop computers [1, 3], producing millions of discarded smartphones each year that end up lying in desk drawers, buried in landfills, or shipped to third-world countries where they are burned to extract precious metals, a process that damages both the health of those involved and the environment.Fortunately, the capabilities of discarded smartphones make them ideal for reuse. Instead of ending up in a landfill, a discarded smartphone could be integrated into a home security system or transformed into a health care device for the elderly. In this paper, we evaluate using discarded smartphones to replace traditional sensor network "motes". Compared with motes, discarded devices have many advantages: price, performance, connectivity, interfaces, and ease of programming. While the main question is whether their energy consumption is low enough to enable harvesting solutions to allow continuous operation, we present preliminary results indicating that this may be possible.

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