操作系统概论（Operating_System_Concepts）课后习题答案.pdf-资料库

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INSTRUCTOR’S MANUAL TO ACCOMPANY OPERATING- SYSTEM CONCEPTS SEVENTH EDITION ABRAHAM SILBERSCHATZ Yale University PETER BAER GALVIN Corporate Technologies GREG GAGNE Westminster College

Preface This volume is an instructor’s manual for the Seventh Edition of Operating- System Concepts, by Abraham Silberschatz, Peter Baer Galvin, and Greg Gagne. It consists of answers to the exercises in the parent text. Although we have tried to produce an instructor’s manual that will aid all of the users of our book as much as possible, there can always be im- provements (improved answers, additional questions, sample test questions, programming projects, alternative orders of presentation of the material, addi- tional references, and so on). We invite you to help us in improving this manual. If you have better solutions to the exercises or other items which would be of use with Operating-System Concepts, we invite you to send them to us for con- sideration in later editions of this manual. All contributions will, of course, be properly credited to their contributor. Internet electronic mail should be addressed to os-book@cs.yale.edu. Physical mail may be sent to Avi Silberschatz, Department nof Computer Sci- ence, Yale University 51 Prospect Street, New Haven, CT 06520, USA. A. S. P. B. G G. G. iii

Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Chapter 1 Chapter 2 Operating-System Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Chapter 3 Threads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Chapter 4 CPU Scheduling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Chapter 5 Process Synchronization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 Chapter 6 Chapter 7 Deadlocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 Chapter 8 Memory Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 Chapter 9 Virtual Memory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 File-Systems Interface. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71 Chapter 10 File-Systems Implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 Chapter 11 Chapter 12 Mass Storage Structure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 I/O Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 Chapter 13 Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99 Chapter 14 Security . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 Chapter 15 Chapter 16 Network Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 Chapter 17 Distributed Communication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117 Chapter 18 Distributed-File Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121 Chapter 19 Multimedia Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127 Embedded Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131 Chapter 20 Chapter 21 The Linux System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137 Chapter 22 Windows XP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145 Inﬂuential Operating Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149 Chapter 23 v

1C H A P T E R Introduction Chapter 1 introduces the general topic of operating systems and a handful of important concepts (multiprogramming, time sharing, distributed system, and so on). The purpose is to show why operating systems are what they are by showing how they developed. In operating systems, as in much of computer science, we are led to the present by the paths we took in the past, and we can better understand both the present and the future by understanding the past. Additional work that might be considered is learning about the particular systems that the students will have access to at your institution. This is still just a general overview, as speciﬁc interfaces are considered in Chapter 3. Exercises 1.1 In a multiprogramming and time-sharing environment, several users share the system simultaneously. This situation can result in various security problems. a. What are two such problems? b. Can we ensure the same degree of security in a time-shared ma- chine as in a dedicated machine? Explain your answer. Answer: a. Stealing or copying one’s programs or data; using system re- sources (CPU, memory, disk space, peripherals) without proper accounting. b. Probably not, since any protection scheme devised by humans can inevitably be broken by a human, and the more complex the scheme, the more difﬁcult it is to feel conﬁdent of its correct implementation. 1

2 Chapter 1 Introduction 1.2 The issue of resource utilization shows up in different forms in differ- ent types of operating systems. List what resources must be managed carefully in the following settings: a. Mainframe or minicomputer systems b. Workstations connected to servers c. Handheld computers Answer: a. Mainframes: memory and CPU resources, storage, network band- width. b. Workstations: memory and CPU resouces c. Handheld computers: power consumption, memory resources. 1.3 Under what circumstances would a user be better off using a time- sharing system rather than a PC or single-user workstation? Answer: When there are few other users, the task is large, and the hardware is fast, time-sharing makes sense. The full power of the system can be brought to bear on the user’s problem. The problem can be solved faster than on a personal computer. Another case occurs when lots of other users need resources at the same time. A personal computer is best when the job is small enough to be exe- cuted reasonably on it and when performance is sufﬁcient to execute the program to the user’s satisfaction. 1.4 Which of the functionalities listed below need to be supported by the operating system for the following two settings: (a) handheld devices and (b) real-time systems. a. Batch programming b. Virtual memory c. Time sharing Answer: For real-time systems, the operating system needs to support virtual memory and time sharing in a fair manner. For handheld systems, the operating system needs to provide virtual memory, but does not need to provide time-sharing. Batch programming is not necessary in both settings. 1.5 Describe the differences between symmetric and asymmetric multipro- cessing. What are three advantages and one disadvantage of multipro- cessor systems? Answer: Symmetric multiprocessing treats all processors as equals, and I/O can be processed on any CPU. Asymmetric multiprocessing has one master CPU and the remainder CPUs are slaves. The master distributes tasks among the slaves, and I/O is usually done by the master only. Multiprocessors can save money by not duplicating power supplies, housings, and peripherals. They can execute programs more quickly and can have increased reliability. They are also more complex in both hardware and software than uniprocessor systems.

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