Technological progress in integrated, low-power, CMOS communication devices and sensors makes a rich design space of networked sensors viable. They can be deeply embedded in the physical world or spread throughout our environment. The missing elements are an overall system architecture and a methodology for systematic advance. To this end, we identify key requirements, develop a small device that is representative of the class, design a tiny event-driven operating system, and show that it provides support for efficient modularity and concurrency-intensive operation. Our operating system fits in 178 bytes of memory, propagates events in the time it takes to copy 1.25 bytes of memory, context switches in the time it takes to copy 6 bytes of memory and supports two level scheduling. The analysis lays a groundwork for future architectural advances.

Fine-grained concurrent object-oriented programming (COOP) models which provide a shared namespace, object-level concurrency and implicit dynamic thread creation can simplify the programming of irregular parallel applications on distributed memory machines. Unfortunately, COOP models are often perceived as inefficient and thus few complete applications have been implemented in COOP languages. In this paper, we study the implementation techniques required to obtain efficient parallel execution of fine-grained COOP languages using a complete, medium-sized protein molecular dynamics program, IC-CEDAR. We found that even given high data locality and achieving good sequential efficiency, an implementation that relies only on thread-oriented compiler and runtime optimizations and software multithreading fails to achieve parallel efficiency. We show that two major sources of overhead --- lack of processor-level data reuse and fine-grained threads for remote object accesses --- contribute to t...