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Lecture notes for the Operating Systems course offered to second-year B.Tech students in the Computer Science & Engineering department at Malla Reddy College of Engineering & Technology. The notes cover topics such as operating system structures, Linux shell, process and CPU scheduling, deadlocks, interprocess communication mechanisms, memory management, and virtual memory. The course objectives include understanding fundamental concepts and techniques of operating systems, studying Linux shell and scheduling, and understanding concepts in deadlocks and process management.
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(Autonomous Institution – UGC, Govt. of India) (Affiliated to JNTUH, Hyderabad, Approved by AICTE - Accredited by NBA & NAAC – ‘A’ Grade - ISO 9001:2015 Certified) Maisammaguda, Dhulapally (Post Via. Hakimpet), Secunderabad – 500100, Telangana State, INDIA.
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II Year B.Tech. CSE- I Sem L/T/P/C 3/-/-/ (R20A0504) OPERATING SYSTEM Course Objectives:
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Introduction Operating System concepts (^1) - 2 Types of Operating Systems, Operating System Components
Operating services (^9) - 13 Introduction to Linux (^13) - 23 II Process & CPU Scheduling Shell Programming 24 - 40 Process concepts and scheduling 40 - 43 Operations on Process, Cooperating Processes (^40) - 43 Threads, Scheduling Criteria 43 - 46 Scheduling Algorithms, Multiprocessor scheduling
Deadlocks & Process Management System Model, Deadlocks Characterization (^55) - 56 Methods for Handling Deadlocks (^56) - 63 The Critical Section Problem (^63) - 69 Classical Problems of Synchronization (^69) - 78 IV (^) Interprocess Communication IPC between processes on a single computer system
shared memory implementation in linux (^83) - 89 Paging & Segmentation (^89) - 122 V (^) File System Interface and Operations Access methods (^123) - 126 Directory Structure. File System Structure (^126) - 139 Allocation methods, Disk Scheduling Algorithms
The Application programs like spreadsheets, Web browsers, word processors, etc. are used to define the ways in which these resources are used to solve the computing problems of the users. And the System program mainly consists of compilers, loaders, editors, OS, etc. The Operating System is mainly used to control the hardware and coordinate its use among the various application programs for the different users. Basically, Computer System mainly consists of hardware, software, and data. OS is mainly designed in order to serve two basic purposes:
1. Simple Batch System In a Batch Operating System, the similar jobs are grouped together into batches with the help of some operator and these batches are executed one by one. For example, let us assume that we have 10 programs that need to be executed. Some programs are written in C++, some in C and rest in Java. Now, every time when we run these programmes individually then we will have to load the compiler of that particular language and then execute the code. But what if we make a batch of these 10 programmes. The benefit with this approach is that, for the C++ batch, you need to load the compiler only once. Similarly, for Java and C, the compiler needs to be loaded only once and the whole batch gets executed. The following image describes the working of a Batch Operating System. Advantages:
Advantages:
Parallel processing requires multiple processors and all the processor works simultaneously in the system. Here, the task is divided into subparts and these subparts are then distributed among the available processors in the system. Parallel processing completes the job on the shortest possible time. All the processors in the parallel processing environment should run on the same operating system. All processors here are tightly coupled and are packed in one casing. All the processors in the system share the common secondary storage like the hard disk. As this is the first place where the programs are to be placed. There is one more thing that all the processors in the system share i.e. the user terminal (from where the user interact with the system). The user need not to be aware of the inner architecture of the machine. He should feel that he is dealing with the single processor only and his interaction with the system would be the same as in a single processor, Advantages
Real-Time Operating System: It is developed for real-time applications where data should be processed in a fixed, small duration of time. It is used in an environment where multiple processes are supposed to be accepted and processed in a short time. RTOS requires quick input and immediate response, e.g., in a petroleum refinery, if the temperate gets too high and crosses the threshold value, there should be an immediate response to this situation to avoid the explosion. Similarly, this system is used to control scientific instruments, missile launch systems, traffic lights control systems, air traffic control systems, etc. This system is further divided into two types based on the time constraints: Hard Real-Time Systems: These are used for the applications where timing is critical or response time is a major factor; even a delay of a fraction of the second can result in a disaster. For example, airbags and automatic parachutes that open instantly in case of an accident. Besides this, these systems lack virtual memory. Soft Real-Time Systems: These are used for application where timing or response time is less critical. Here, the failure to meet the deadline may result in a degraded performance instead of a disaster. For example, video surveillance (cctv), video player, virtual reality, etc. Here, the deadlines are not critical for every task every time. Advantages of real-time operating system: o The output is more and quick owing to the maximum utilization of devices and system o Task shifting is very quick, e.g., 3 microseconds, due to which it seems that several tasks are executed simultaneously o Gives more importance to the currently running applications than the queued application o It can be used in embedded systems like in transport and others. o It is free of errors.
o Memory is allocated appropriately. Disadvantages of real-time operating system: o A fewer number of tasks can run simultaneously to avoid errors. o It is not easy for a designer to write complex and difficult algorithms or proficient programs required to get the desired output. o Specific drivers and interrupt signals are required to respond to interrupts quickly. o It may be very expensive due to the involvement of the resources required to work. An operating system is an interface which provides services to both the user and to the programs. It provides an environment for the program to execute. It also provides users with the services of how to execute programs in a convenient manner. The operating system provides some services to program and also to the users of those programs. The specific services provided by the OS are off course different. Following are the common services provided by an operating system:
Both the processes can be on one computer or a different computer, but are connected through a computer network. 5) Error handling An error is one part of the system that may cause malfunctioning of the complete system. The operating system constantly monitors the system for detecting errors to avoid some situations. This give relives to the user of the worry of getting an error in the various parts of the system causing malfunctioning. The error can occur anytime and anywhere. The error may occur anywhere in the computer system like in CPU, in I/O devices or in the memory hardware. There are some activities that are performed by an operating system: The OS continuously checks for the possible errors. The OS takes an appropriate action to correct errors and consistent computing. 6) Resource management When there are multiple users or multiple jobs running at the same time resources must be allocated to each of them. There are some major activities that are performed by an operating system: The OS manages all kinds of resources using schedulers. CPU scheduling algorithm is used for better utilization of CPU. 7) Protection The owners of information stored in a multi-user computer system want to control its use. When several disjoints processes execute concurrently it should not be possible for any process to interfere with another process. Every process in the computer system must be secured and controlled. Operating system can be implemented with the help of various structures. The structure of the OS depends mainly on how the various common components of the operating system are interconnected and melded into the kernel. Depending on this we have following structures of the operating system: Simple structure: Such operating systems do not have well defined structure and are small, simple and limited systems. The interfaces and levels of functionality are not well separated. MS-DOS is an example of such operating system. In MS-DOS application programs are able to access the basic I/O routines. These types of operating system cause the entire system to crash if one of the user programs fails. Diagram of the structure of MS-DOS is shown below.
Advantages of Simple structure: It delivers better application performance because of the few interfaces between the application program and the hardware. Easy for kernel developers to develop such an operating system. Disadvantages of Simple structure: The structure is very complicated as no clear boundaries exists between modules. It does not enforce data hiding in the operating system. Layered structure: An OS can be broken into pieces and retain much more control on system. In this structure the OS is broken into number of layers (levels). The bottom layer (layer 0) is the hardware and the topmost layer (layer N) is the user interface. These layers are so designed that each layer uses the functions of the lower level layers only. This simplifies the debugging process as if lower level layers are debugged and an error occurs during debugging then the error must be on that layer only as the lower level layers have already been debugged. The main disadvantage of this structure is that at each layer, the data needs to be modified and passed on which adds overhead to the system. Moreover careful planning of the layers is necessary as a layer can use only lower level layers. UNIX is an example of this structure.
files/ user files are arranged. Shell - Linux provides a special interpreter program which can be used to execute commands of the operating system. It can be used to do various types of operations, call application programs etc. Security - Linux provides user security using authentication features like password protection/ controlled access to specific files/ encryption of data. Linux Advantages
and setup programs. Popular Linux distributions come with tools that make installation of additional software very user friendly as well.
