Real-time systems play a considerable role in our society, and they cover a spectrum from the very simple to the very complex. Examples of current real-time systems include the control of domestic appliances like washing machines and televisions, the control of automobile engines, telecommunication switching systems, military command and control systems, industrial process control, flight control systems, and space shuttle and aircraft avionics.
All of these involve gathering data from the environment, processing of gathered data, and providing timely response. A concept of time is the distinguishing issue between real-time and non-real-time systems. When a usual design goal for non-real-time systems is to maximize system's throughput, the goal for real-time system design is to guarantee, that all tasks are processed within a given time. The taxonomy of time introduces special aspects for real-time system research.
Real-time operating systems are an integral part of real-time systems. Future systems will be much larger, more widely distributed, and will be expected to perform a constantly changing set of duties in dynamic environments. This also sets more requirements for future real-time operating systems.
This seminar has the humble aim to convey the main ideas on Real Time System and Real Time Operating System design and implementation
Design issue of Real Time Systems
Real-time systems are defined as those systems in which the correctness of the system depends not only on the logical result of computation, but also on the time at which the results are produced. A common misconception is to consider, that real-time computing is equivalent to fast computing. In traditional non-real-time computer systems, the performance goal is throughput: as many tasks should be processed as possible in given time period. Real-time systems have a different goal to meet: as many tasks as possible should be executed so, that they will complete and produce results before their time limit expires. In other words, the behavior of real-time system must be predictable  in all situations.
To archieve predictability, all components of the real-time system must be time bounded. A predictability of the system depends on many different aspects.
The computer hardware must not introduce unpredictable delays into program execution. For example, caching and swapping as well as DMA cycle stealing are often problematic when determining process execution timing.
An operating system must have a predictable behavior in all situations. Often the common-purpose operating systems, like UNIX, are too large and complex, and they have too much unpredictability. Thus, a special microkernel operating systems like the Chorus microkernel  have been designed for real-time purposes.
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