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Introduction to Operating Systems

Introduction to Operating Systems. Chapter 1. Key concepts in chapter 1. Multilevel implementation also called layered Resources Hardware: provided to the OS Logical (a.k.a. virtual): created by the OS Resource management transformation multiplexing time and space.

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Introduction to Operating Systems

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  1. Introduction to Operating Systems Chapter 1 Crowley OS Chap. 1

  2. Key concepts in chapter 1 • Multilevel implementation • also called layered • Resources • Hardware: provided to the OS • Logical (a.k.a. virtual): created by the OS • Resource management • transformation • multiplexing • time and space Crowley OS Chap. 1

  3. Levels in a computer system Crowley OS Chap. 1

  4. Design: Two-level implementation • Two-level implementation • Lower level is a problem-specific language • Upper level solves the problem at hand • Lower level is reusable • In operating systems • mechanism: lower level of basic functions, does not change • policy: upper level policy decisions, easy to change and experiment Crowley OS Chap. 1

  5. Operating system functions • Resource manager • manage hardware and software resources • Virtual machine manager • implement a virtual machine for processes to run in • a nicer environment than the bare hardware Crowley OS Chap. 1

  6. Hardware resources • Processor: execute instructions • Memory: store programs and data • Input/output (I/O)controllers: transfer to and from devices • Disk devices: long-term storage • Other devices: conversion between internal and external data representations Crowley OS Chap. 1

  7. Hardware resources Crowley OS Chap. 1

  8. Resource management functions • Transforming physical resources to logical resources • Making the resources easier to use • Multiplexing one physical resource to several logical resources • Creating multiple, logical copies of resources • Scheduling physical and logical resources • Deciding who gets to use the resources Crowley OS Chap. 1

  9. Types of multiplexing • Time multiplexing • time-sharing • scheduling a serially-reusable resource among several users • Space multiplexing • space-sharing • dividing a multiple-use resource up among several users Crowley OS Chap. 1

  10. Virtual computers • Processor virtualized to processes • mainly time-multiplexing • Memory virtualized to address spaces • space and time multiplexing • Disks virtualized to files • space-multiplexing • transforming Crowley OS Chap. 1

  11. Multiple virtual computers Crowley OS Chap. 1

  12. Time-multiplexing the processor Crowley OS Chap. 1

  13. Space-multiplexing memory Crowley OS Chap. 1

  14. Time-multiplexing I/O devices Crowley OS Chap. 1

  15. Space-multiplexing the disk Crowley OS Chap. 1

  16. Do we need an OS? • Not always • Some programs run “stand-alone” • But they are very useful • Reusable functions • Easier to use than the bare hardware Crowley OS Chap. 1

  17. decisecond: 10-1 sec. centiecond: 10-2 sec. millisecond: 10-3 sec. microsecond: 10-6 sec. nanosecond: 10-9 sec. picosecond: 10-12 sec. femptosecond: 10-15 sec. attoseond: 10-18 sec. dekabyte: 101 bytes hectobyte: 102 bytes kilobyte: 103 bytes megabyte: 106 bytes gigabyte: 109 bytes terabyte: 1012 bytes petabyte: 1015 bytes exabyte: 1018 bytes Metric prefixes Crowley OS Chap. 1

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