What's 'real' about real-time systems?

A real-time system is typically a concurrent (or distributed) system whose computations and actions must satisfy some real-time constraints. Guaranteeing that such a system will in fact meet its constraints can thus be viewer either in terms of some extended model of program correctness or as a problem of scheduling, eg one of establishing a feasible schedule. However, the crucial distinction between real-time and other concurrent programs is not merely that of time, but that the former must execute on a system with limited resources. In this paper, we give an informal account of a semantic model of programs which may execute with limited resources. In this paper, we give an informal account of a semantic model of programs which may execute with limited resources: thus, the model can serve both as the basis for a formal specification system for real-time programs and to characterise real-time scheduling problems