Tracking the changing dynamics of object-oriented frameworks[5], design patterns[7], architectural styles[8], and subsystems during the development and reuse cycle can aid producing complex systems. Unfortunately, current object-oriented programming tools are relatively oblivious to the rich architectural abstractions in a system.This paper shows that architecture-oriented visualization, the graphical presentation of system statics and dynamics in terms of its architectural abstractions, is highly beneficial in designing complex systems. In addition, the paper presents architecture-aware instrumentation, a new technique for building efficient on-line instrumentation to support architectural queries. We demonstrate the effectiveness and performance of the scheme with case studies in the design of the Choices object-oriented operating system.