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Real-Time Operating Systems • In real-time applications, users need computer to perform some actions in a timely p y manner – To control activities in an external system, or to participate in them • If application takes too long to respond to an activity, a failure can occur in the external system – Response requirement indicates the largest value of response time for which the system can function perfectly – Deadline: time by which action should be performed 3.25 25 Hard and Soft Real-Time Systems • A hard real-time system meets response requirements under all conditions – It is typically dedicated to processing real-time applications – E.g., guidance and control applications • A soft real-time system makes best effort to meet response requirement of a real-time application – Cannot C t guarantee t that th t it will ill be b able bl tto meett it • Meets requirements in a probabilistic manner – E.g., reservation and banking applications 3.26 26 1 Features of a Real-Time Operating System 3.27 27 Modern Operating Systems 3.28 28 2 Summary • A computing environment consists of a computer system its interfaces with other systems system, systems, and the services provided by its OS to users and programs – Evolved with advances in computer technology • Each computing environment was serviced by a separate class of operating systems – Batch processing systems • Automate A t t transition t iti between b t jobs j b – Multiprogramming operating system • Priority-based preemptive scheduling – Time-sharing operating systems • Round-robin scheduling with time-slicing 3.29 29 Summary (continued) – Real-time operating systems • Priority-based Priority based scheduling and deadline-aware deadline aware scheduling – Distributed operating system • Lets programs share resources across network – Modern operating system • Modern computing environment has elements of all the classic computing environments • Uses most ost co concepts cepts and a d techniques tec ques in classic c ass c ope operating at g systems 3.30 30 3