On the duality of operating system structures

Many operating system designs can be placed into one of two very rough categories, depending upon how they implement and use the notions of process and synchronization. One category, the "Message-oriented System," is characterized by a relatively small, static number of processes with an explicit message system for communicating among them. The other category, the "Procedure-oriented System," is characterized by a large, rapidly changing number of small processes and a process synchronization mechanism based on shared data.In this paper, it is demonstrated that these two categories are duals of each other and that a system which is constructed according to one model has a direct counterpart in the other. The principal conclusion is that neither model is inherently preferable, and the main consideration for choosing between them is the nature of the machine architecture upon which the system is being built, not the application which the system will ultimately support.