Page 15 - DCAP608_REAL TIME SYSTEMS

Real Time Systems

Notes  An OS that can absolutely guarantee a maximum time for the operations it performs is
referred to as hard real-time.

 Hard real-time systems are designed to absolutely guarantee that a task will execute
within a certain worst-case timeframe.
 For projects involving safety or systems that could result in a large investment in the
event of failure, hard real-time is often a requirement.
 Soft real-time systems are designed to satisfy your timing requirements most of the time
but without absolute certainty.

 Hard real-time systems guarantee (when programmed correctly) that a deadline will be
consistently met, while soft real-time systems may periodically exceed the deadline.

1.6 Keywords

Hard Real-time System: It is hardware or software that must operate within the confines of a
stringent deadline.
Predictability: It is the condition of real-time system has to react to all possible events in a
predictable way.
Real Time: The term is used to describe a number of different computer features. For example,
real-time operating systems are systems that respond to input immediately.
Real-time System: It is a real-time system when it can support the execution of applications with
time constraints on that execution.

Soft Real-time System: It can be a vending machine rising cost for lateness of results as it will
take longer to treat a customer when the performance of the vending machine is degrading, less
customers pay at this machine which results in less profits for the shop owner.

Timeliness: It is a condition of real-time system that to meet deadlines it is required that the
application has to finish certain tasks within the time boundaries.

1.7 Review Questions

1. What do you understand by the term “real-time”?

2. Describe the structure and importance of real-time system.
3. Explain the concept of real-time operating system.
4. How is the concept of real-time different from the traditional notion of time? Explain your
answer using a suitable example.
5. Discuss in brief hard and soft real-time system.
6. Identify the key differences between hard real-time, soft real time, and firm real-time
systems.
7. Give an example of a soft real-time task and a non-real-time task.
8. Explain the key difference between the characteristics of soft real-time task and a non-real-
time task.
9. Define timeline in real-time system.
10. What are timing constraints?

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