Abstract: An apparatus for monitoring events. One embodiment monitors complex SOC-specific Off-module transactions using logic on the core PMU that is decoupled from the data sources supported by the SOC. The PMU's new logic works directly on data source information passed in from the SOC in the form of a Performance Monitoring Data Encoding, and makes the encoding available to key capabilities like the precise sampling logic and the load latency logic. In this way, events corresponding to complex Off-module transactions can be precisely sampled or timed, which was previously impractical. To facilitate the tuning process, the encodings are mapped to event names representing transactions implemented by specific SOCs. The names and encodings are then provided in an event list to drivers used by performance analysis tools. Although this is a microarchitectural feature, the need to deliver useful transaction names to performance monitoring tools makes this also a software-visible feature.