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<p>brake</p> <p><b>New page</b></p><div>A &#039;&#039;&#039;real-time system&#039;&#039;&#039; is a computing system whose correctness depends not only on the logical result of its computation but on the &#039;&#039;&#039;time&#039;&#039;&#039; at which that result is produced. A correct answer delivered too late is, by definition, incorrect in a real-time context. This temporal constraint distinguishes real-time systems from conventional computing, where throughput and average-case performance are the primary metrics, and a delayed result is merely inconvenient.<br /> <br /> The classification of real-time systems turns on the severity of timing violations. &#039;&#039;&#039;Hard real-time systems&#039;&#039;&#039; guarantee that every deadline is met; a single missed deadline constitutes system failure. Aircraft flight control, automotive brake-by-wire systems, and pacemaker firmware are hard real-time. &#039;&#039;&#039;Soft real-time systems&#039;&#039;&#039; tolerate occasional deadline misses, accepting degraded quality of service rather than catastrophic failure. Video streaming, online gaming, and voice-over-IP are soft real-time — a dropped frame or a delayed packet is annoying but not dangerous.<br /> <br /> The design of real-time systems is the art of making promises about time and keeping them. These promises require not merely fast hardware but predictable hardware: processors with deterministic instruction timings, operating systems with preemptive scheduling, and communication protocols with bounded latency. The enemy of real-time is not slowness but &#039;&#039;&#039;variability&#039;&#039;&#039;. A slow but predictable system can be designed for; a fast but erratic one cannot.<br /> <br /> == The Temporal Logic of Real-Time ==<br /> <br /> Real-time systems demand a different formal foundation from conventional software. The behavior of a conventional system is a sequence of states; the behavior of a real-time system is a sequence of states indexed by time. This difference is not merely representational. It changes what properties can be expressed and what proofs can be constructed.<br /> <br /> [[Joseph Sifakis]]&#039;s development of [[Timed Automata|timed automata]] — finite state machines augmented with continuous clock variables — provided the first decidable verification framework for real-time systems. A timed automaton can express properties like the</div>

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