Real Time System.

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REAL TIME SYSTEM

The term is used to describe a number of different  features. For example, real-time  are  that respond to  immediately. They are used for such tasks as navigation, in which the computer must react to a steady flow of new information without interruption. Most general-purpose operating systems are not real-time because they can take a few seconds, or even minutes, to react.

Real time can also refer to events simulated by a computer at the same speed that they would occur in real life. In  , for example, a real-time  would display  moving across the  at the same speed that they would actually move.

Various real-time operating systems are evaluated by benchmarking and testing as well as extended with particular real-time features. Since standard PC-based systems and corresponding components are becoming more and more important for embedded applications, one major research topic is to develop distributed/parallel real-time environments with of-the-shelf embedded hardware and real-time operating systems.

A distributed real-time system

TYPES OF REAL-TIME SYSTEM

1.    Hard real-time

       Systems where it is absolutely imperative that responses occur within the specified deadline.

         The properties of a hard real-time system are:

  1. no lateness is accepted under circumstances
  2. useless results if late
  3. catastrophic failure if deadline missed
  4. cost of missing deadline is infinitely high

       Ex.:  - flight control systems.

           - fly by wire control system of an aircraft

- an automobile system that generates ignition timing must produce a spark at a certain precise instant, even if there are other tasks that the computer must carry out to avert disastrous results.

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2.    Soft real-time

Systems where will still function correctly if deadlines are occasionally missed.

The characteristics of a soft real-time system are:

  1. rising cost for lateness of results
  2. acceptance of lower performance for lateness

       Ex.: - data acquisition system.

          - a vending machine

                 - network interface subsystem, we can recovered from a missed thing by using   one or another network protocol asking to resend the missed thing

             

3.    Real real-time 

       Systems which are hard real-time ...

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