Note for Operating Systems - OS by Nataraju A.B

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15ECS553 … OPERATING SYSTEM (CBCS) Lecture Notes (Ver 1.1) Subject: OPERATING SYSTEM (CBCS) Subject Code: 15EC553 Semester: 5th B.E(ECE) OPERATING SYSTEM B.E., V Semester, Electronics & Communication Engineering / Telecommunication Engineering [As per Choice Based Credit System (CBCS) scheme] Subject Code Number of Lecture Hours/Week Total Number of Lecture Hours IA Marks 20 15EC553 03 Exam Marks 80 40 (8 Hours / Module) Exam Hours 03 CREDITS – 03 Module-1 : Introduction to Operating Systems Introduction to Operating Systems OS, Goals of an OS, Operation of an OS, Computational Structures, Resource allocation techniques, Efficiency, System Performance and User Convenience, Classes operating System, Batch processing, Multi programming, Time Sharing Systems, Real Time and distributed Operating Systems (Topics from Sections 1.2, 1.3, 2.2 to 2.8 of Text). Module-2 Process Management Process Management: OS View of Processes, PCB, Fundamental State Transitions, Threads, Kernel and User level Threads, Non-preemptive scheduling- FCFS and SRN, Preemptive Scheduling- RR and LCN, Long term, medium term and short term scheduling in a time sharing system (Topics from Sections 3.3, 3.3.1 to 3.3.4, 3.4, 3.4.1, 3.4.2 , 4.2, 4.3, 4.4.1 of Text). Module-3 : Memory Management Memory Management: Contiguous Memory allocation, Non-Contiguous Memory Allocation, Paging, Segmentation, Segmentation with paging, Virtual Memory Management, Demand Paging, Paging Hardware, VM handler, FIFO, LRU page replacement policies (Topics from Sections 5.5 to 5.9, 6.1 to 6.3, except Optimal policy and 6.3.1 of Text). Module-4 : File Systems File Systems: File systems and IOCS, File Operations, File Organizations, Directory structures, File Protection, Interface between File system and IOCS, Allocation of disk space, Implementing file access (Topics from Sections 7.1 to 7.8 of Text). Module-5 : Message Passing and Deadlocks Message Passing and Deadlocks: Overview of Message Passing, Implementing message passing, Mailboxes, Deadlocks, Deadlocks in resource allocation, Resource state modeling, Deadlock detection algorithm, Deadlock Prevention (Topics from Sections 10.1 to 10.3, 11.1 to 11.5 of Text). Question paper pattern: The question paper will have ten questions Each full question consists of 16 marks. There will be 2 full questions (with a maximum of four sub questions) from each module. Each full question will have sub questions covering all the topics under a module The students will have to answer 5 full questions, selecting one full question from each module Text Book: 1. Operating Systems – A concept based approach, by Dhamdare, TMH, 2nd edition. Reference Books: 1. Operating systems concepts, Silberschatz and Galvin, John Wiley India Pvt. Ltd, 5th edition, 2001. 2. Operating system–internals and design system, William Stalling, Pearson Education, 4th edition, 2006. 3. Design of operating systems, Tannanbhaum, TMH, 2001. Page |1

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15ECS553 … OPERATING SYSTEM (CBCS) Lecture Notes (Ver 1.1) ACKNOWLEDGEMENT I would like to express my heartfelt gratitude for all the authors of the referred books mentioned below 1. Operating Systems – A concept based approach, by Dhamdare, TMH, 2nd edition. 2. Operating systems concepts, Silberschatz and Galvin, John Wiley India Pvt. Ltd, 5th edition, 2001. 3. Operating system–internals and design system, William Stalling, Pearson Education, 4th edition, 2006. 4. Design of Operating Systems, Tanenbaum, TMH, 2001. I would also take this opportunity to thank all those who have directly or indirectly provided suggestions and guidelines for the smooth accomplishment of this work. Note: Majority of the content in this work has been taken from the text books mentioned above with some more details added from my own understanding about the topics…. Page |2

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15ECS553 … OPERATING SYSTEM (CBCS) Lecture Notes (Ver 1.1) Module-1 : Introduction to Operating Systems : OS, Goals of an OS, Operation of an OS, Computational Structures, Resource allocation techniques, Efficiency, System Performance and User Convenience, Classes operating System, Batch processing, Multi programming, Time Sharing Systems, Real Time and distributed Operating Systems (Selected Topics from Ch -1, 2 of Text 1). The operating system (OS) is the intermediary between users and the computer system. It provides the services and features present in abstract views of all its users through the computer system. Abstract views of an Operating system (User’s perspective) A question such as “What is an OS?” is likely to evoke different answers, depending on the user’s interest. For example,  To a school or college student, the OS is the software that permits access to the Internet.  To a programmer, the OS is the software that makes it possible to develop programs on a computer system.  To a user of an application package, the OS is simply the software that makes it possible to use the package.  To a technician in, say, a computerized chemical plant, the OS is the invisible component of a computer system that controls the plant. The operating system is the intermediary between users and the computer system. It provides the services and features present in abstract views of all its users through the computer system. It also enables the services and features to evolve over time as users’ needs change. An operating system (OS) is system software that manages computer hardware and software resources and provides common services for computer programs. An individual user has an abstract view of the computer system, a view that takes in only those features that the user considers important. Abstract view of an Operating System (Designer’s perspective) The typical functionalities are as follows: Page |3

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15ECS553 … OPERATING SYSTEM (CBCS) Lecture Notes (Ver 1.1) • User interface: The user interface accepts commands to execute programs and use resources and services provided by the operating system. It is either a command line interface, as in Unix or Linux, which displays a command prompt to the user and accepts a user command, or is a graphical user interface (GUI), as in the Windows operating system, which interprets mouse clicks on icons as user commands. • Non-kernel routines: These routines implement user commands concerning execution of programs and use of the computer’s resources; they are invoked by the user interface. • Kernel: The kernel is the core of the OS. It controls operation of the computer and provides a set of functions and services to use the CPU, memory, and other resources of the computer. The functions and services of the kernel are invoked by the non kernel routines and by user programs. Goals of an OS: The fundamental goals of an operating system are:  Efficient use: Ensure efficient use of a computer’s resources.  User convenience: Provide convenient methods of using a computer system.  Noninterference: Prevent interference in the activities of its users. The goals of efficient use and user convenience sometimes conflict. For example, emphasis on quick service could mean that resources like memory have to remain allocated to a program even when the program is not in execution; however, it would lead to inefficient use of resources. When such conflicts arise, the designer has to make a trade-off to obtain the combination of efficient use and user convenience that best suits the environment. This is the notion of effective utilization of the computer system. Interference with a user’s activities may take the form of illegal use or modification of a user’s programs or data, or denial of resources and services to a user. Such interference could be caused by both users and nonusers, and every OS must incorporate measures to prevent it. Efficient Use An operating system must ensure efficient use of the fundamental computer system resources of memory, CPU, and I/O devices such as disks and printers. Poor efficiency can result if a program does not use a resource allocated to it, e.g., if memory or I/O devices allocated to a program remain idle. Such a situation may have a snowballing effect: Since the resource is allocated to a program, it is denied to other programs that need it. These programs cannot execute, hence resources allocated to them also remain idle. In addition, the OS itself consumes some CPU and memory resources during its own operation, and this consumption of resources constitutes an overhead that also reduces the resources available to user programs. To achieve good efficiency, the OS must minimize the waste of resources by programs and also minimize its own overhead. Efficient use of resources can be obtained by monitoring use of resources and performing corrective actions when necessary. However, monitoring use of resources increases the overhead, which lowers efficiency of use. In practice, operating systems that emphasize efficient use limit their overhead by Page |4