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Gurwinder Kaur, Lovely Professional University Unit 1: Concept of Real-time System

Unit 1: Concept of Real-time System Notes

CONTENTS
Objectives
Introduction

1.1 Real-time Systems
1.2 Hard Real-time Systems
1.3 Soft Real-time Systems

1.4 Hard Versus Soft Real-time System
1.5 Summary
1.6 Keywords
1.7 Review Questions
1.8 Further Readings

Objectives

After studying this unit, you will be able to:
 Describe the Utility of an Operating System

 Define the Term Real-time System
 Understand the Structure and Components of Real-time System
 Explain Hard and Soft Real-time System
 Describe the Differences between Hard and Soft Real-time System

Introduction

An Operating System (OS) is responsible for managing the hardware resources of a computer
and hosting applications that run on the computer. An RTOS performs these tasks, but is also
specially designed to run applications with very precise timing and a high degree of reliability.
This can be especially important in measurement and automation systems where downtime is
costly or a program delay could cause a safety hazard. To be considered “real-time”, an operating
system must have a known maximum time for each of the critical operations that it performs (or
at least be able to guarantee that maximum most of the time). Some of these operations include
OS calls and interrupt handling. Operating systems that can absolutely guarantee a maximum
time for these operations are commonly referred to as “hard real-time”, while operating systems
that can only guarantee a maximum most of the time are referred to as “soft real-time”. In
practice, these strict categories have limited usefulness – each RTOS solution demonstrates
unique performance characteristics and the user should carefully investigate these characteristics.

1.1 Real-time Systems

A real-time system is one that must process information and produce a response within a
specified time, else risk severe consequences, including failure. That is, in a system with a real-
time constraint it is no good to have the correct action or the correct answer after a certain

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