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We present Synchroscalar, a tile-based

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This article reports on a study of the value master' s students in a principal preparation program placed on a variety of instructional strategies. The aspiring principals completed a survey with fixed-response and open-ended items. The students' most valued class discussions were about how their personal experiences related to the class topic and how to apply the topic to practice. The class activities they valued the most highly were problem solving, simulations, small-group discussions, and whole-group discussions. The highest rated out-of-class assignments included writing reflective papers, conducting interviews and observations, and performing leadership activities in schools. The types of readings the master' s students most appreciated were case studies and journal articles. In describing their "outstanding professor," the aspiring principals focused on the professor' s personal qualities, creation of a positive learning environment, and constructivist teaching.

Despite the high costs associated with processor manufacturing, the typical chip is used for only a fraction of its expected lifetime. Reusing processors would create a "food chain"of electronic devices that amortizes the energy required to build chips over several computing generations.T he past decade has seen unprecedented growth in the number of electronic devices available to consumers. Many of these devices, from com puters to set-top boxes to cell phones, require sophisticated semiconductors such as CPUs and memory chips. The economic and environmental costs of producing these processors for new and continually upgraded devices are enormous.Because the semiconductor manufacturing process uses highly purified silicon, the energy required is quite high-about 41 megajoules (MJ) for a dynamic random access memory (DRAM) die with a die size of 1.2 cm 2 . 1To illustrate the macroeconomic impact of this energy cost, Japan's semiconductor industry is expected to con sume 1.7 percent of the country's electricity budget by 2015.2 Approximately 600 kilograms of fossil fuels are needed to generate enough energy to create a 1-kilogram semiconductor.3 Furthermore, according to chip con sortium Sematech, foundry energy consumption also continues to increase. 4 In terms of environmental impact, 72 grams of toxic chemicals are used to create a 1.2 cm 2 DRAM die. The semiconductor industry manufactured 28.4 million cm 2 of such dies in 2000, which translates to 1.7 billion kilo grams of hazardous material.2 Due to the increasing num ber of semiconductor devices manufactured each year, semiconductor disposal costs are likewise increasing.Despite these costs, the typical processor is used for only a fraction of its expected lifetime. While rapid tech nological advances are quickly making silicon obsolete, chips could be removed from recycled electronics and reused for less demanding computing tasks. A proces sor reuse strategy would create a "food chain" of com puting devices that amortizes the energy required to build processors-particularly low-power, embedded processors-over several computing generations. PROCESSOR LIFETIME ENERGY CONSUMPTIONThe lifetime energy consumption of a processor or memory chip can be expressed as the sum of the • manufacturing energy cost, including the creation of silicon wafers, the chemical and lithography processes, and chip assembly and packaging; and • utilization energy cost.A comparative analysis of these two components reveals that the energy required to manufacture a processor can dominate the energy consumed over the processor's life time. Manufacturing energy costSemiconductor manufacturing involves many steps, from crystal growth to dicing to packaging. Total energy cost can be expressed as E manufacturing = E die + E assembly . E die is the energy required to manufacture the die of the processor or memory chip and includes wafer growth, epitaxial layering, applying photo resists, etching,

croarchitecture have on the application. To manage this interaction between the microarchitec ture and applications, we leverage the following key ob

As circuit geometries continue to shrink, and supply voltages re main relatively constant, circuit wearout becomes a concern. We propose that the relative reliability of the circuits of a processor be exposed to the operating system, and be managed by a credit-based wearout monitor. This wearout monitor receives dynamic updates of the reliability of circuits through the use of stability detector cir cuits that are small enough to be widely deployed. We find that through the combined use of the wearout monitor and stability de tectors, we can efficiently and accurately manage the reliability of a processor, and re-coup the performance of a processor that would otherwise be lost when processors are over-provisioned to meet an expected lifetime. We simulate a 16 core DSP with a wearout mon itor and stability detectors on a mix of four different media algo rithms. Using the wearout monitor and stability detectors, we find that by reducing average performance by only 5%, we can increase the lifetime of the processor by 46%.