Our goal is to identify the key architectural and design issues related to Sensor Networks (SNs), evaluate the proposed solutions, and to outline the most challenging research directions. The evaluation has three scopes - individual components on SN nodes (processor, communication, storage, sensors, actuators, and power supply), node level and networked system level. The special emphasis is placed on architecture and system software, and on new challenges related to the usage of new types of components in networked systems. The evaluation is guided by anticipated technology trends and both current and future applications. The main conclusion of the analysis is that the architectural and synthesis emphasis will be shifted from computation and to some extent communication components to sensors and actuators.