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Os concepts

  1. 1. OPERATING SYSTEMS S5R Name of Faculty: Reena Murali Dept. of Computer science RIT
  2. 2. Introduction and Overview What is an operating system? How have operating systems evolved? Why study operating systems?
  3. 3. What is an Operating System? • Not easy to define precisely… Users Applications Operating System Hardware • OS: compilers databases word processors CPU memory I/O devices Everything in system that isn’t an application or hardware • OS: Software that converts hardware into a useful form for applications
  4. 4. What is the role of the OS? • Role #1: Resources provider • What is a resource? – Anything valuable (e.g., CPU, memory, disk)
  5. 5. What is the role of the OS? • Role #2: Resource coordinator (I.e., manager) • Advantages of resource coordinator – Virtualize resources so multiple users or applications can share – Protect applications from one another – Provide efficient and fair access to resources
  6. 6. What Functionality belongs in OS? • No single right answer • Desired functionality depends on outside factors – OS must adapt to both user expectations and technology changes
  7. 7. OS Concepts
  8. 8. A Computer System:
  9. 9. • OS can be viewed as Users Applications Operating System Hardware compilers databases word processors CPU memory I/O devices
  10. 10. OPERATING SYSTEM OVERVIEW Humans Program Interface User Programs O.S. Interface O.S. Hardware Interface/ Privileged Instructions Disk/Tape/Memory The Layers Of A System
  11. 11. Conclusion
  12. 12. An Operating system is • An interface between users and hardware - an environment "architecture” • Allows convenient and efficient usage of resources (Gives each user a slice of the resources) • Provides information protection • Acts as a control program.
  13. 13. Example OS
  14. 14. Common Operating Systems • DOS • Windows 95,98,2000, NT, XP, Vista … • UNIX / LINUX (Distributions like Red Hat, Suse, Debian, Ubuntu…. ), MacOS
  15. 15. Evolution of OS
  16. 16. Evolution of Operating Systems • • • • • • • • Early Systems (1950) Simple Batch Systems (1960) Multiprogrammed Batch Systems (1970) Time-Sharing (1970) Personal/Desktop Systems (1980) Multiprocessor Systems (1980) Networked/Distributed Systems (1980) Real-Time (1970) and Handheld (1990)
  17. 17. Batch Processing Batch: Group of jobs submitted together – Operator collects jobs; orders efficiently; runs one at a time • Advantages – Keep machine busy while programmer thinks – Improves throughput and utilization • Disadvantages – User must wait until batch is done for results – Machine idle when job is reading from cards and writing to printers
  18. 18. Multiprogrammed Systems • Goal of OS – Improve performance by always running a job – Keep multiple jobs resident in memory – When job waits for disk I/O, OS switches to another job • OS Functionality – Job scheduling policies – Memory management and protection • Advantage: Improves throughput and utilization • Disadvantage: Machine not interactive
  19. 19. Interactive Multiprogramming
  20. 20. Time Sharing Systems (TSS) • Batch multiprogramming does not support interaction with users. • In time sharing systems multiple users simultaneously access the system through terminals . • Processor’s time is shared among multiple users.
  21. 21. Why does Time-Sharing work? • Because of slow human reaction time, a typical user needs 2 seconds of processing time per minute. • Then many users should be able to share the same system without noticeable delay in the computer reaction time. • The user should get a good response time.
  22. 22. Personal/Desktop Systems • Personal computers – dedicated to a single user. computer system • I/O devices – keyboards, mice, display screens, small printers. • May run several different types of operating systems (Windows, MacOS, UNIX, Linux)
  23. 23. Other Systems • Multi User Systems • Multi Tasking Systems
  24. 24. Networked Systems • Requires networking infrastructure. • Local area networks (LAN) or Wide area networks (WAN). • May be either Centralized Sever or Client-Server or Peer-to-Peer (P2P) systems.
  25. 25. Local Area Network (LAN) structure
  26. 26. Wide Area Network (WAN) structure
  27. 27. Client/Server Environment
  28. 28. Client-Sever Systems
  29. 29. Peer-To-Peer (P2P) Systems
  30. 30. • **Networked/Distributed Systems computation Distribute resources and the among several physical processors. • Loosely coupled system: – each processor has its own local memory. – processors communicate with one another through various communications lines. • Advantages: – Resources Sharing – Computation speed up – load sharing – Reliability
  31. 31. Networked/Distributed System Structure node 1 node 2 disk disk processors processors disk disk network node 3 node N disk disk processors processors disk … disk
  32. 32. Networked/Distributed Operating Systems • Network Operating System (NOS): – provides mainly file sharing. – Each computer runs independently from other computers on the network. • Distributed Operating System (DOS): – gives the impression there is a single operating system controlling the network. – network is mostly transparent – it’s a powerful virtual machine.
  33. 33. Real-Time Systems (RTS) • Note that not all Operating Systems are general-purpose systems. • Real-Time (RT) systems are dedicated systems that need to adhere to deadlines , i.e., time constraints. • Correctness of the computation depends not only on the logical result but also on the time at which the results are produced.
  34. 34. Hard Real-Time Systems • Hard real-time system: – Must meet its deadline. • Often used as a control device in a dedicated application: – Industrial control – Robotics • Secondary storage limited or absent, data stored in short term memory, or read-only memory (ROM).
  35. 35. Soft Real-Time Systems • Soft real-time system: – Deadline desirable but not mandatory. – Limited utility in industrial control or robotics. – Useful in modern applications (multimedia, virtual reality) requiring advanced operating-system features.
  36. 36. Handheld Systems • Handheld systems are also dedicated. – Personal Digital Assistants (PDAs). – Cellular telephones. • Issues: – Limited memory – Slow processors – Small display screens – Support for multimedia (images, video)
  37. 37. Migration of OS Concepts and Features
  38. 38. Operating-System Concepts • • • • functions of OS Operating System Services System Calls OS Structure
  39. 39. Functions of OS • • • • • • • • Process Management Main Memory Management File Management I/O System Management Secondary Management Networking Protection System Command-Interpreter System
  40. 40. Process Management • A process is a program in execution. A process needs certain resources, including CPU time, memory, files, and I/O devices, to accomplish its task. • The operating system is responsible for the following activities in connection with process management. – Process creation and deletion. – process suspension and resumption. – Provision of mechanisms for: • process synchronization • process communication
  41. 41. Main-Memory Management • Memory is a large array of words or bytes, each with its own address. It is a repository of quickly accessible data shared by the CPU and I/O devices. • Main memory is a volatile storage device. It loses its contents in the case of system failure. • The operating system is responsible for the following activities in connections with memory management: – Keep track of which parts of memory are currently being used and by whom. – Decide which processes to load when memory space becomes available. – Allocate and deallocate memory space as needed.
  42. 42. File Management • A file is a collection of related information defined by its creator. Commonly, files represent programs (both source and object forms) and data. • The operating system is responsible for the following activities in connections with file management: – File creation and deletion. – Directory creation and deletion. – Mapping files onto secondary storage. – File backup on stable (nonvolatile) storage media.
  43. 43. I/O System Management • The I/O system consists of: – A buffer-caching system – A general device-driver interface – Drivers for specific hardware devices
  44. 44. Secondary-Storage Management • Since main memory (primary storage) is volatile and too small to accommodate all data and programs permanently, the computer system must provide secondary storage to back up main memory. • Most modern computer systems use disks as the principle on-line storage medium, for both programs and data. • The operating system is responsible for the following activities in connection with disk management: – Free space management – Storage allocation – Disk scheduling
  45. 45. Networking (Distributed Systems) • A distributed system is a collection processors that do not share memory or a clock. Each processor has its own local memory. • The processors in the system are connected through a communication network. • Communication takes place using a protocol. • A distributed system provides user access to various system resources. • Access to a shared resource allows: – Computation speed-up – Increased data availability – Enhanced reliability
  46. 46. Protection System • Protection refers to a mechanism for controlling access by programs, processes, or users to both system and user resources. • The protection mechanism must: – distinguish between authorized and unauthorized usage. – specify the controls to be imposed. – provide a means of enforcement.
  47. 47. Command-Interpreter System • Many commands are given to the operating system by control statements which deal with: – process creation and management – I/O handling – secondary-storage management – main-memory management – file-system access – protection – networking
  48. 48. Command-Interpreter System (Cont.) • The program that reads and interprets control statements is called variously: – command-line interpreter – shell (in UNIX) Its function is to get and execute the next command statement.
  49. 49. Additional Operating System Functions Additional functions exist not for helping the user, but rather for ensuring efficient system operations. • Resource allocation – allocating resources to multiple users or multiple jobs running at the same time. • Accounting – keep track of and record which users use how much and what kinds of computer resources for account billing or for accumulating usage statistics. • Protection – ensuring that all access to system resources is controlled.
  50. 50. OS SERVICES
  51. 51. Operating System Services • Program execution – system capability to load a program into memory and to run it. • I/O operations – since user programs cannot execute I/O operations directly, the operating system must provide some means to perform I/O. • File-system manipulation – program capability to read, write, create, and delete files. • Communications – exchange of information between processes executing either on the same computer or on different systems tied together by a network. Implemented via shared memory or message passing. • Error detection – ensure correct computing by detecting errors in the CPU and memory hardware, in I/O devices, or in user programs.
  52. 52. System Calls
  53. 53. System Calls • System calls provide the interface between a running program and the operating system. – Generally available as assembly-language instructions. – Languages defined to replace assembly language for systems programming allow system calls to be made directly (e.g., C, C++) • Three general methods are used to pass parameters between a running program and the operating system. – Pass parameters in registers. – Store the parameters in a table in memory, and the table address is passed as a parameter in a register. – Push (store) the parameters onto the stack by the program, and pop off the stack by operating system.
  54. 54. Passing of Parameters As A Table
  55. 55. Types of System Calls • • • • • Process control File management Device management Information maintenance Communications
  56. 56. Components of OS
  57. 57. The OS Shell • Defines interface between OS and users – Windows GUI – UNIX command line – UNIX users can choose among a variety of shells • csh is the “C shell” • tcsh is an enhanced “C shell”
  58. 58. OS Shell interface Users Users O/S shell Users
  59. 59. The OS Kernel • The internal part of the OS is often called the kernel • Kernel Components – File Manager – Device Drivers – Memory Manager – Scheduler – Dispatcher
  60. 60. OS File Manager • Maintains information about the files that are available on the system • Where files are located in mass storage, their size and type and their protections, what part of mass storage is available • Files usually allowed to be grouped in directories or folders. Allows hierarchical organization.
  61. 61. OS Device Drivers • Software to communicate with peripheral devices or controllers • Each driver is unique • Translates general requests into specific steps for that device
  62. 62. OS Memory Manager • Responsible for coordinating the use of the machine’s main memory • Decides what area of memory is to be allocated for a program and its data • Allocates and deallocates memory for different programs and always knows what areas are free
  63. 63. OS Scheduler • Maintains a record of processes that are present, adds new processes, removes completed processes – memory area(s) assigned – priority – state of readiness to execute (ready/wait)
  64. 64. OS Dispatcher • Ensures that processes that are ready to run are actually executed • Time is divided into small (50 ms) segments called a time slice • When the time slice is over, the dispatcher allows scheduler to update process state for each process, then selects the next process to run
  65. 65. OS structures
  66. 66. Design Approaches • Three common approaches: – Kernel Approach • monolithic kernel • microkernel • exokernel – Layered Approach – Virtual Machine Approach
  67. 67. Kernel approach
  68. 68. Kernel Based Approach • • • • Kernel contains a collection of primitives which are used to build the OS OS implements policy, Kernel implements mechanisms The advantage is performance, the disadvantage are complexity and maintainability Why use this approach? If you have a relatively “small” kernel the gains in performance and efficiency outweigh the disadvantages. User Applications User Apps Sys Services kernel-user interface kernel-user interface kernel (privileged) kernel (privileged) hw-sw interface hw-sw interface hardware hardware References: 1. Brinch Hansen, P., "The Nucleus of a Multiprogramming System", Communications of the ACM, Apr. 1970, pp. 238-241. 2. D. Ritchie, and K. Thompson, “The UNIX Time-Sharing System”, Communications of the ACM, Vol. 17, No. 7, Jul. 1974, pp. 365-375. 3. Wulf, W., E. Cohen, W. Corwin, A. Jones, R. Levin, C. Pierson, and F. Pollack, "HYDRA: The Kernel of a Multiprocessor Operating System", Communications of the ACM, June 1974, pp. 337-345.
  69. 69. 1. Monolithic Operating System
  70. 70. MS-DOS System Structure • MS-DOS – written to provide the most functionality in the least space: – not divided into modules (monolithic). – Although MS-DOS has some structure, its interfaces and levels of functionality are not well separated.
  71. 71. MS-DOS System Structure
  72. 72. UNIX System Structure • • UNIX – limited by hardware functionality, the original UNIX OS had limited structuring. The UNIX OS consists of two separable parts: 1. Systems Programs: 2. The Kernel: • Consists of everything below the system-call interface and above the physical hardware • Provides the file system, CPU scheduling, memory management, and other operating-system functions; a large number of functions for one level.
  73. 73. UNIX System Structure
  74. 74. Traditional UNIX Kernel [Bach86]
  75. 75. 2. Microkernel System Structure (1) • Move as much functionality as possible from the kernel into “user” space. • Only a few essential functions in the kernel – primitive memory management (address space) – I/O and interrupt management – Inter-Process Communication (IPC) – basic scheduling • Other OS services are provided by processes running in user mode (vertical servers) – device drivers, file system, virtual memory…
  76. 76. 2. Microkernel System Structure (2) • Communication takes place between user modules using message passing. • But a performance penalty caused by replacing service calls with message exchanges between process. • More flexibility, extensibility, portability and reliability (details in next 4 slides).
  77. 77. Microkernel Operating System
  78. 78. Benefits of a Microkernel Organization (1) • Extensibility/Reliability – modular design. – easy to add services. – small microkernel can be rigorously tested. • Portability – changes needed to port the system to a new processor is done in the microkernel in the other services. not
  79. 79. Benefits of Microkernel Organization (2) • Distributed system support – message are sent without knowing what the target machine is. • Object-oriented operating system – components are objects with clearly defined interfaces that can be interconnected to form software.
  80. 80. Mach 3 Microkernel Structure
  81. 81. Windows NT Client-Server Structure
  82. 82. Windows NT 4.0 Architecture
  83. 83. The Neutrino Microkernel
  84. 84. 3. Exokernel • Takes micro-kernel to the extreme • Services implemented as user space library linked against application. • Only a minimum of functionality is implemented in the kernel, such as context switching and MMU management. • Export hardware resources that may be managed by user-level applications while the kernel implements the protection mechanism • Apps may optimize to a given hardware platform or create new resource abstractions References: • D. R. Engler M. F. Kaashoek J. O'Toole, Jr., “Exokernel: an operating system architecture for application-level resource management”, Proceedings of the fifteenth ACM symposium on Operating systems principles, pp. 251-266, Copper Mountain, Colorado, 1995.
  85. 85. Layered Approach
  86. 86. Layered Approach • The operating system is divided into a number of layers (levels), each built on top of lower layers. The bottom layer (layer 0), is the hardware; the highest (layer N) is the user interface. • With modularity, layers are selected such that each uses functions (operations) and services of only lower layers.
  87. 87. General OS Layers
  88. 88. Layered Operating System
  89. 89. Older Windows System Layers
  90. 90. OS/2 Layer Structure
  91. 91. Layered vs. Microkernel Architecture
  92. 92. Virtual Machine Approach • Virtual software layer over hardware • Illusion of multiple instances of hardware • Supports multiple instances of OSs VM1 VM2 VM3 VM4 Virtual machine software Hardware References: • Seawright, L., and R. MacKinnon, "VM/370 - A Study of Multiplicity and Usefulness", IBM Systems Journal, 1979, pp. 4-17.
  93. 93. Virtual Machines • A virtual machine takes the layered approach to its logical conclusion. It treats hardware and the operating system kernel as though they were all hardware. • A virtual machine provides an interface identical to the underlying bare hardware. • The operating system creates the illusion of multiple processes, each executing on its own processor with its own (virtual) memory.
  94. 94. OS Summary • Shell -- interface to user • File Manager -- manages mass memory • Device Drivers -- communicate with peripherals • Memory Manager -- manages main memory • Scheduler & Dispatcher -- manage processes
  95. 95. Different Operating Systems on the Same Machine ? • It is possible to have more than one operating system available to be used on a machine. • Only one operating system is run at a time, though. • Examples: – VAX -- VMS or Ultrix – PCs -- DOS, Windows, or Linux
  96. 96. Utilities • Operating systems usually come with some associated utility programs • UNIX usually has the text editors emacs and vi (and sometimes pico) • UNIX has its own sort utility • UNIX has its own mail utility
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