Real-Time systems

Real-Time systems

• Real-Time systems span several domains of computer science.
• They are defense and space systems, networked multimedia systems, embedded automotive electronics etc.
• In a real-time system the correctness of the system behaviour depends not only the logical results of the computations, but also on the physical instant at which these results are produced.
• A real-time system changes its state as a function of physical time, e.g., a chemical reaction continues to change its state even after its controlling computer system has stopped.
• Based on this a real-time system can be decomposed into a set of subsystems i.e., the controlled object, the real-time computer system and the human operator.
• A real-time computer system must react to stimuli from the controlled object within time intervals dictated by its environment.
• The instant at which a result is produced is called a deadline. If the result has utility even after the deadline has passed, the deadline is classified as soft, otherwise it is firm.
• If a catastrophe could result if a firm deadline is missed, the deadline is hard. Commands and Control systems, Air traffic control systems are examples for hard real-time systems.
• On-line transaction systems, airline reservation systems are soft real-time systems