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Note for Advanced operating system - AOS by Siddharth Rajput

  • Advanced Operating System - AOS
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UNIT VII: OPERATING SYSTEM LAST SIX YEARS' GATE ANALYSIS 7 Number of questions 6 5 Marks 1 Marks 2 Total number of questions 4 3 2 1 0 2015 2014 2013 2012 2011 2010 Concepts on which questions were asked in the previous six years Year Concept 2015 Shared variable, SCAN algorithm, Page replacement, Processes, Process synchronization, Deadlock, Process scheduling, TLB, Best fit algorithm, Page table 2014 Page Frames, Deadlock, Translation Lookaside Buffer (TLB), Disk Scheduling Algorithm 2013 Scheduling, Disk Management, Semaphores, Concurrent Processes, Memory Management 2012 System Calls (Fork), Scheduling Algorithms, Concurrent Processes 2011 DMA Concept, Interrupts, Lightweight Processes, User–Kernel Mode, Scheduling Algorithms 2010 Deadlock, Critical Section, Page table, Concurrent Process Concept Chapter 7.indd 325 4/9/2015 10:01:07 AM

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Chapter 7.indd 326 4/9/2015 10:01:07 AM

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CHAPTER 7 OPERATING SYSTEM Syllabus: Operating system: Processes, Threads, Inter-process communication, Concurrency, Synchronization, Deadlock, CPU scheduling, Memory management and virtual memory, File systems, I/O systems, Protection and security 7.1  INTRODUCTION An operating sysem (OS) can be defined as an intermediate program between the user and the computer hardware. On the user end, it handles application programs and at the other end it makes use of system call(s) to instruct the hardware to perform certain task as instructed by the user. There are different types of operating systems to accomplish various tasks. Mainframe operating systems are designed to optimize hardware utilization. The real-time operating systems are designed for timeliness, the time-sharing systems are designed for efficient usage of the system and other resources. Some of the examples of OS are: UNIX, Linux (different flavors, such as, Redhat, Suse, Fedora, Debian etc.), MacOS, Microsoft Windows, etc. Nowadays, the mobiles that we use are also equipped with operating system. Some of the  well-known OS for mobiles are – Symbian and Android. Chapter 7.indd 327 The function of the operating systems is to provide an environment in which a user can execute his/her commands in a convenient and efficient manner. Operating system is also called resource allocator. The placement of operating systems in a computing environment is shown in Fig. 7.1. User User application Operating system Physical device (hardware) Figure 7.1 |   Location of an operating system in a ­computing environment. 4/9/2015 10:01:07 AM

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328     Chapter 7:  Operating System  System Call is a request made by a user program to get the service of an operating system. 7.2.2  Multiprogramming Operating System To consider the “inside view” of the system, the OS is written as a collection of procedures, each of which can call any other, whenever required. Each parameter has a well-defined interface with input parameters and output results. A simplified layered structure of Dijkstra’s “THE” operating system is shown in Fig. 7.2: A single user cannot keep either the CPU or the I/O devices busy at all times. Multiprogramming increases CPU utilization by organizing jobs so that the CPU is not idle at any time (Fig. 7.4). Jobs to be executed are maintained in the memory simultaneously and the OS switches among these jobs for their execution. When one job waits for some input (WAIT state), the CPU switches to another job. This process is followed for all jobs in memory. When the wait for the first job is over, the CPU is back to serve it. The CPU will be busy till all the jobs have been executed. Thus, increasing the CPU utilization and throughput. LAYER FUNCTION 5 The operator (user) 4 User programs 3 Input/output management 2 Operator-process communication 1 Memory management 0 Process allocation and multiprogramming Job 2 Job 1 CPU Job 4 Figure 7.2 |   Simplified structure of Dijkstra’s THE operating system. JOB 3 Job 3 Job 5 JOB 1 OS I/O Memory Figure 7.4 |   A multiprogramming operating system. 7.2  TYPES OF OPERATING SYSTEM 7.2.1  Batch Operating System In a batch operating system, tasks are submitted to a pool, and only after the completion of one job, the next job is executed (Fig. 7.3). In this system, the CPU idle time (free time) is high and throughput of the system is low. Throughput is the number of jobs executed per unit time. 7.2.3  Multitasking Operating System Multitasking system is the extension of multiprogramming system. In this system, jobs will be executed in the time-sharing mode. It uses CPU scheduling and multiprogramming techniques to provide a small portion of a timeslot to each user. Each user has at least one separate program in memory. 7.2.4  Multiprocessor Operating System Multiprocessor operating system consists of more than one processor for execution (Fig. 7.5). It improves the throughput of the system and it is also more reliable than the single processor system because if one processor breaks down then the other can share the load of that processor (Table 7.1). Job 1 Job 2 CPU Job 3 Job 4 ....... ....... Batch CPU 1 CPU 2 CPU 3 CPU 4 I/O Job n OS Memory Figure 7.3 |   A batch operating system. Chapter 7.indd 328 Memory Figure 7.5 |   A multiprocessor operating system. 4/9/2015 10:01:09 AM

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