Real Time Operating System

  • Real-time systems are defined as those systems in which the correctness of the system depends not only on the logical result produced, but also the time at which the result produced.
  • User convenience and resource utilization are secondary concern to these systems.
  • Real time systems have many events that must be accepted and processed in a short time or within certain deadline.
  • Such applications include:
    • Rocket lunching
    • Flight control
    • Robotics
    • Telephone switching equipment
    • Fire and smoke sensor etc.
  • Real time systems are classified into two categories:
    • Hard Real Time System
    • Soft Real Time System

Hard Real Time System

  • A system is said to be hard real time system if the deadline is not met the system is said to have failed.
  • Penalty due to missing deadline is a higher order of magnitude than the reward in meeting the deadline
  • The task deadlines are of the order of micro or milliseconds.
  • Examples: : Industrial control applications
    • On-board computers
    •  Robots
  • These systems guarantee that critical tasks should be completed on time.

Soft Real Time System

A system is said to be soft real time system, If a deadline is missed, the system does not fail.

  • Only the performance of the system is said to have degraded.
  • The utility of a result decreases with time after the deadline.
  • Penalty often lesser magnitude than reward
    Examples: Railway reservation system, video on demand system

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