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Overview of Operating Systems

Chapters 1 and 2. Overview of Operating Systems. Introduction. Twin aims of an operating system are: User convenience System performance Performance measures depend on the computing environment Number of requests serviced per unit time, etc. Introduction. Fundamental tasks of an OS

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Overview of Operating Systems

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  1. Chapters 1 and 2 Overview of Operating Systems

  2. Introduction • Twin aims of an operating system are: • User convenience • System performance • Performance measures depend on the computing environment • Number of requests serviced per unit time, etc

  3. Introduction • Fundamental tasks of an OS - Management of Programs * Organize their execution by sharing the CPU * Ensure good user service and efficient use - Management of Resources * Efficient allocation/de-allocation without constraining user programs - Security and Protection * Ensure absence of interference with programs and resources by entities within and outside the OS

  4. Overview of security and protection threats

  5. OS and the Computer System • In this module, we study - Fundamental features of computer systems that are important to an OS * Memory hierarchy * Interrupt structure * I/O organization - Fundamentals of how a program interacts with an OS

  6. Memory utilization during operation of an OS

  7. Model of a Computer System

  8. Fields of Program Status Word (PSW)

  9. (a) Program (b) State of CPU after executing COMPARE instruction

  10. Memory hierarchy containing cache, main memory and disk

  11. Memory hierarchy • Cache memory * Organization – Cache block or cache line -- Inclusive or exclusive -- Direct, fully associative, set associative * Different levels of caches – Why? How many levels? * Cache hit ratio – What factors influence it? • Main memory * Memory protection * Virtual memory?

  12. Memory protection using bound registers

  13. A schematic of virtual memory operation

  14. Input/Output organization • Involvement of the CPU in I/O operations -- Should be the minimum possible due to imbalance between CPU and I/O speeds -- CPU should be free to execute instructions while I/O operations are in progress • Different I/O modes -- Programmed I/O -- Interrupt I/O -- Direct memory access (DMA)

  15. Input Output Modes

  16. Interrupts • An interrupt signals the occurrence of an event to the CPU • The CPU is diverted to execution of an OS routine • Different classes of interrupts convey occurrence of different kinds of events

  17. Classes of Interrupts

  18. The interrupt action

  19. Steps in interrupt action

  20. An operating system in its computing environment

  21. Interrupt driven operation of a kernel

  22. System Call • A system call is a request made by a program through a special instruction called a `software interrupt’ instruction • The software interrupt is a program interrupt • When a software interrupt occurs, the interrupt hardware transfers control to a routine of the OS • The operand of the software interrupt instruction indicates what kind of request is being made by a program

  23. System Calls

  24. Interrupt processing and scheduling

  25. Simple and nested interrupt processing

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