Software Tema 1, Apuntes de Ingeniería de Telecomunicaciones

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Operating System Concepts – 8th^ Edition Silberschatz, Galvin and Gagne ©

Chapter 1: Introduction

Chapter 1: Introduction

 What Operating Systems Do

 Computer-System Organization

 Computer-System Architecture

 Operating-System Structure

 Operating-System Operations

 Process Management

 Memory Management

 Storage Management

 Protection and Security

 Distributed Systems

 Special-Purpose Systems

 Computing Environments

 Open-Source Operating Systems

What is an Operating System?

 A program that acts as an intermediary between a user of a computer and the computer hardware

 Operating system goals:

 Execute user programs and make solving user problems easier  Make the computer system convenient to use  Use the computer hardware in an efficient manner

Computer System Structure

 Computer system can be divided into four components:

 Hardware – provides basic computing resources  CPU, memory, I/O devices  Operating system  Controls and coordinates use of hardware among various applications and users  Application programs – define the ways in which the system resources are used to solve the computing problems of the users  Word processors, compilers, web browsers, database systems, video games  Users  People, machines, other computers

What Operating Systems Do

 Depends on the point of view

 Users want convenience, ease of use

 Don’t care about resource utilization

 But shared computer such as mainframe or minicomputer must keep all users happy

 Users of dedicate systems such as workstations have dedicated resources but frequently use shared resources from servers

 Handheld computers are resource poor, optimized for usability and battery life

 Some computers have little or no user interface, such as embedded computers in devices and automobiles

Operating System Definition

 OS is a resource allocator

 Manages all resources  Decides between conflicting requests for efficient and fair resource use

 OS is a control program

 Controls execution of programs to prevent errors and improper use of the computer

Computer Startup

 bootstrap program is loaded at power-up or reboot

 Typically stored in ROM or EPROM, generally known as firmware  Initializes all aspects of system  Loads operating system kernel and starts execution

Computer System Organization

 Computer-system operation

 One or more CPUs, device controllers connect through common bus providing access to shared memory  Concurrent execution of CPUs and devices competing for memory cycles

Common Functions of Interrupts

 Interrupt transfers control to the interrupt service routine generally, through the interrupt vector , which contains the addresses of all the service routines

 Interrupt architecture must save the address of the interrupted instruction

 Incoming interrupts are disabled while another interrupt is being processed to prevent a lost interrupt

 A trap is a software-generated interrupt caused either by an error or a user request

 An operating system is interrupt driven

Interrupt Handling

 The operating system preserves the state of the CPU by storing registers and the program counter

 Determines which type of interrupt has occurred:

 polling  vectored interrupt system

 Separate segments of code determine what action should be taken for each type of interrupt

I/O Structure

 After I/O starts, control returns to user program only upon I/O completion  Wait instruction idles the CPU until the next interrupt  Wait loop (contention for memory access)  At most one I/O request is outstanding at a time, no simultaneous I/O processing

 After I/O starts, control returns to user program without waiting for I/O completion  System call – request to the operating system to allow user to wait for I/O completion  Device-status table contains entry for each I/O device indicating its type, address, and state  Operating system indexes into I/O device table to determine device status and to modify table entry to include interrupt

Direct Memory Access Structure

 Used for high-speed I/O devices able to transmit information at close to memory speeds

 Device controller transfers blocks of data from buffer storage directly to main memory without CPU intervention

 Only one interrupt is generated per block, rather than the one interrupt per byte

Storage Hierarchy

 Storage systems organized in hierarchy

 Speed  Cost  Volatility

 Caching – copying information into faster storage system; main memory can be viewed as a cache for secondary storage

Storage-Device Hierarchy