Abstract: Due to its high efficiency and extensive versatility, active message is becoming the main communication mechanism on massively parallel processors. Greatly optimized messaging layers can be implemented on a variety of architectures. This paper analyzes the essence and the implementation technology of active messages on a conventional message passing system, a remote procedure call system, a message driven system, and a direct memory access system. We compare the influences on the implementation technology given by different system organizations. We consider that how to support active message better in hardware of communication unit is an important research aspect.