OPERATING

1 OPERATINGSYSTEMCONCEPTSNINTH EDITION OPERATINGSYSTEMCONCEPTSABRAHAM SILBERSCHATZYale UniversityPETER BAER GALVINP luribus NetworksGREG GAGNEW estminster CollegeNINTH EDITION Vice President and Executive Publisher Don Fowley Executive Editor Beth Lang Golub Editorial Assistant Katherine Willis Executive Marketing Manager Christopher Ruel Senior Production Editor Ken Santor Cover and title page illustrations Susan Cyr Cover Designer Madelyn Lesure Text Designer Judy Allan This book was set in Palatino by the author using LaTeX and printed and bound by Courier Kendallville. The cover was printed by Courier. Copyright 2013, 2012, 2008 John Wiley & Sons, Inc. All rights reserved.

2 No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, scanning or otherwise, except as permitted under Sections 107 or 108 of the 1976 United States Copyright Act, without either the prior written permission of the Publisher, or authorization through payment of the appropriate per copy fee to the Copyright Clearance Center, Inc. 222 Rosewood Drive, Danvers, MA 01923, (978)750 8400, fax (978)750 4470. Requests to the Publisher for permission should be addressed to the Permissions Department, John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030 (201)748 6011, fax (201)748 6008, E Mail: Evaluation copies are provided to qualified academics and professionals for review purposes only, for use in their courses during the next academic year.

3 These copies are licensed and may not be sold or transferred to a third party. Upon completion of the review period, please return the evaluation copy to Wiley. Return instructions and a free of charge return shipping label are available at Outside of the United States, please contact your local representative. Founded in 1807, John Wiley & Sons, Inc. has been a valued source of knowledge and understanding for more than 200 years, helping people around the world meet their needs and fulfill their aspirations. Our company is built on a foundation of principles that include responsibility to the communities we serve and where we live and work. In 2008, we launched a Corporate Citizenship Initiative, a global effort to address the environmental, social, economic, and ethical challenges we face in our business.

4 Among the issues we are addressing are carbon impact, paper specifications and procurement, ethical conduct within our business and among our vendors, and community and charitable support. For more information, please visit our website: ISBN: 978 1 118 06333 0 ISBN BRV: 978 1 118 12938 8 Printed in the United States of America 10 9 8 7 6 5 4 3 2 1 To my children, Lemor, Sivan, and Aaronand my NicoletteAvi SilberschatzTo Brendan and Ellen,and Barbara, Anne and Harold, and Walter and RebeccaPeter Baer GalvinTo my Mom and Dad,Greg GagnePrefaceOperating systems are an essential part of any computer system. Similarly,a course on OPERATING systems is an essential part of any computer scienceeducation.

5 This field is undergoing rapid change, as computers are nowprevalent in virtually every arena of day-to-day life from embedded devicesin automobiles through the most sophisticated planning tools for governmentsand multinational firms. Yet the fundamental concepts remain fairly clear, andit is on these that we base this wrote this book as a text for an introductory course in OPERATING systemsat the junior or senior undergraduate level or at the first-year graduate level. Wehope that practitioners will also find it useful. It provides a clear description oftheconceptsthat underlie OPERATING systems. As prerequisites, we assume thatthe reader is familiar with basic data structures, computer organization, anda high-level language, such as C or Java.

6 The hardware topics required for anunderstanding of OPERATING systems are covered in Chapter 1. In that chapter,we also include an overview of the fundamental data structures that areprevalent in most OPERATING systems. For code examples, we use predominantlyC, with some Java, but the reader can still understand the algorithms withouta thorough knowledge of these are presented using intuitive descriptions. Important theoreticalresults are covered, but formal proofs are largely omitted. The bibliographicalnotes at the end of each chapter contain pointers to research papers in whichresults were first presented and proved, as well as references to recent materialfor further reading.

7 In place of proofs, figures and examples are used to suggestwhy we should expect the result in question to be fundamental concepts and algorithms covered in the book are oftenbased on those used in both commercial and open-source OPERATING aim is to present these concepts and algorithms in a general setting thatis not tied to one particular OPERATING system. However, we present a largenumber of examples that pertain to the most popular and the most innovativeoperating systems, including linux , Microsoft Windows, Apple MacOS X,andSolaris. We also include examples of both Android and iOS, currently the twodominant mobile OPERATING organization of the text reflects our many years of teaching courses onoperating systems, as well as curriculum guidelines published by theIEEE viiviiiPrefaceComputing Society and the Association for Computing Machinery (ACM).

8 Consideration was also given to the feedback provided by the reviewers ofthe text, along with the many comments and suggestions we received fromreaders of our previous editions and from our current and former of This BookThe text is organized in eight major parts: Overview. Chapters 1 and 2 explain what OPERATING systems are, whatthey do, and how they are designed and constructed. These chaptersdiscuss what the common features of an OPERATING system are and what anoperating system does for the user. We include coverage of both traditionalPCand server OPERATING systems, as well as OPERATING systems for mobiledevices. The presentation is motivational and explanatory in nature.

9 Wehave avoided a discussion of how things are done internally in thesechapters. Therefore, they are suitable for individual readers or for studentsin lower-level classes who want to learn what an OPERATING system iswithout getting into the details of the internal algorithms. Process management. Chapters 3 through 7 describe the process conceptand concurrency as the heart of modern OPERATING systems. Aprocessis the unit of work in a system. Such a system consists of a collectionofconcurrentlyexecuting processes, some of which are OPERATING -systemprocesses (those that execute system code) and the rest of which are userprocesses (those that execute usercode).

10 These chapters cover methods forprocess scheduling, interprocess communication, process synchronization,and deadlock handling. Also included is a discussion of threads, as wellas an examination of issues related to multicore systems and parallelprogramming. Memory management. Chapters 8 and 9 deal with the management ofmain memory during the execution of a process. To improve both theutilization of theCPUand the speed of its response to its users, thecomputer must keep several processes in memory. There are many differentmemory-management schemes, reflecting various approaches to memorymanagement, and the effectiveness of a particular algorithm depends onthe situation.