Determining and substantiating the capabilities and limitations of complex hardware/software systems are tasks of increasing importance to computer manufacturers and users alike. The identification and elimination of many system inefficiencies have been impossible due to the lack of a factual basis in the design and utilization of the system. A significant step in solving this problem has been the development of instrumentation which provides a profile of executed instructions in a non-degraded system; in particular, special attention has been given to inefficiencies in the operating system. Initial favorable results indicate that a step in the right direction has been taken toward providing an instrumentation capability which provides a factual basis for the enhancement of prresent systems and for the design of future systems.