Chapter 1: IntroductionDhamdhere: Operating Systems— A Concept-Based Approach Slide No: 1 Copyright ©2005 Overview of Operating Systems Chapters 1 and 2

Chapter 1: IntroductionDhamdhere: Operating Systems— A Concept-Based Approach Slide No: 2 Copyright ©2005 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

Chapter 1: IntroductionDhamdhere: Operating Systems— A Concept-Based Approach Slide No: 3 Copyright ©2005 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

Chapter 1: IntroductionDhamdhere: Operating Systems— A Concept-Based Approach Slide No: 4 Copyright ©2005 Overview of security and protection threats

Chapter 1: IntroductionDhamdhere: Operating Systems— A Concept-Based Approach Slide No: 5 Copyright ©2005 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

Chapter 1: IntroductionDhamdhere: Operating Systems— A Concept-Based Approach Slide No: 6 Copyright ©2005 Memory utilization during operation of an OS

Chapter 1: IntroductionDhamdhere: Operating Systems— A Concept-Based Approach Slide No: 7 Copyright ©2005 Model of a Computer System

Chapter 1: IntroductionDhamdhere: Operating Systems— A Concept-Based Approach Slide No: 8 Copyright ©2005 Fields of Program Status Word (PSW)

Chapter 1: IntroductionDhamdhere: Operating Systems— A Concept-Based Approach Slide No: 9 Copyright ©2005 (a) Program (b) State of CPU after executing COMPARE instruction

Chapter 1: IntroductionDhamdhere: Operating Systems— A Concept-Based Approach Slide No: 10 Copyright ©2005 Memory hierarchy containing cache, main memory and disk

Chapter 1: IntroductionDhamdhere: Operating Systems— A Concept-Based Approach Slide No: 11 Copyright ©2005 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?

Chapter 1: IntroductionDhamdhere: Operating Systems— A Concept-Based Approach Slide No: 12 Copyright ©2005 Memory protection using bound registers

Chapter 1: IntroductionDhamdhere: Operating Systems— A Concept-Based Approach Slide No: 13 Copyright ©2005 A schematic of virtual memory operation

Chapter 1: IntroductionDhamdhere: Operating Systems— A Concept-Based Approach Slide No: 14 Copyright ©2005 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)

Chapter 1: IntroductionDhamdhere: Operating Systems— A Concept-Based Approach Slide No: 15 Copyright ©2005 Input Output Modes

Chapter 1: IntroductionDhamdhere: Operating Systems— A Concept-Based Approach Slide No: 16 Copyright ©2005 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

Chapter 1: IntroductionDhamdhere: Operating Systems— A Concept-Based Approach Slide No: 17 Copyright ©2005 Classes of Interrupts

Chapter 1: IntroductionDhamdhere: Operating Systems— A Concept-Based Approach Slide No: 18 Copyright ©2005 The interrupt action

Chapter 1: IntroductionDhamdhere: Operating Systems— A Concept-Based Approach Slide No: 19 Copyright ©2005 Steps in interrupt action

Chapter 1: IntroductionDhamdhere: Operating Systems— A Concept-Based Approach Slide No: 20 Copyright ©2005 An operating system in its computing environment

Chapter 1: IntroductionDhamdhere: Operating Systems— A Concept-Based Approach Slide No: 21 Copyright ©2005 Interrupt driven operation of a kernel

Chapter 1: IntroductionDhamdhere: Operating Systems— A Concept-Based Approach Slide No: 22 Copyright ©2005 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

Chapter 1: IntroductionDhamdhere: Operating Systems— A Concept-Based Approach Slide No: 23 Copyright ©2005 System Calls

Chapter 1: IntroductionDhamdhere: Operating Systems— A Concept-Based Approach Slide No: 24 Copyright ©2005 Interrupt processing and scheduling

Chapter 1: IntroductionDhamdhere: Operating Systems— A Concept-Based Approach Slide No: 25 Copyright ©2005 Simple and nested interrupt processing