Real Time System and Its Types Explained

Real Time System

A real time system is a software system where the correct functioning of the system depends on the results produced by the system and the time at which these results are produced.

  • Time is critical so real-time systems must respond within specified times.
  • Systems which monitor and control their environment.
  • Inevitably associated with hardware devices:
  • Sensors: Collect data from the system environment
  • Actuators: Change the system’s environment in some way

 real time system The real time system can be classified as:

1.Soft real time system:

A soft real-time system is a system whose operation is degraded if results are not produced according to the specified timing requirements.

2. Hard real time system:

A hard real-time system is a system whose operation is incorrect if results are not produced according to the timing specification.real time system model

Fig: An embedded real time system model

System Elements


  • Sensor control processes: Collect information from sensors. May buffer information collected in response to a sensor stimulus.
  • Data processor: Carries out processing of collected information and computes the system response.
  • Actuator control processes: Generates control signals for the actuators. Sensor and actuator processes

Fig: Sensor and actuator processes

System Design:

  • System Design comprises of both the hardware and the software associated with system.
  • Design decisions should be made on the basis on non-functional system requirements.
  • Hardware delivers better performance but potentially longer development and less scope for change.

1 Real Time System Design Process

  • Identify the stimuli to be processed and the required responses to these stimuli.
  • For each stimulus and response, identify the timing constraints.
  • Aggregate the stimulus and response processing into concurrent processes. A process may be associated with each class of stimulus and response.
  • Design algorithms to process each class of stimulus and response. These must meet the given timing requirements.
  • Design a scheduling system which will ensure that processes are started in time to meet their deadlines.
  • Integrate using a real-time operating system.


2 Timing Constraints

  • May require extensive simulation and experiment to ensure that these are met by the system.
  • May mean that certain design strategies such as object-oriented design cannot be used because of the additional overhead involved.
  • May mean that low-level programming language features have to be used for performance reasons.


3 Real Time system Modeling

  • The effect of a stimulus in a real-time system may trigger a transition from one state to another.
  • Finite state machines can be used for modeling real-time systems.
  • However, FSM models lack structure. Even simple systems can have a complex model.
  • The UML includes notations for defining state machine models.Petrol pump state model

Fig: Petrol pump state model



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A Soon-to-be Computer Engineer by profession, he has profound devotion to add Data Scientist as a prefix to his name. He’s been to the nooks of the web (at least of the surface web) and planning to add some real figures in his pocket!

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