Time-triggered (TT) distributed real-time computing systems are moving into the mainstream for the implementation of safety-critical applications in the aerospace and automotive sectors. This paper introduces the basic principles of a time-triggered real-time computing system, and elaborates on the benefits that can be gained from the availability of a global time base in general, and in specifying the linking interfaces of components in particular. It describes the concept of a temporal firewall that forms a fully specified operational interface of a component. The most important contribution of the TT-paradigm is the capability to precisely specify operational interfaces in the temporal domain and thus establish a sound basis for the composability of a design and the reuse of components in distributed real-time systems.