Operating System Concepts - Introduction PDF

Chapter 1: Introduction
What Operating Systems Do
Computer-System Or...

Chapter 1: Introduction
What Operating Systems Do
Computer-System Organization
Computer-System Architecture
Operating-System Structure Chapter 1: Introduction
Operating-System Operations
Process Management
Memory Management
Storage Management
Protection and Security
Kernel Data Structures
Computing Environments
Open-Source Operating Systems Operating System Concepts – 9th Edit9on Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition 1.2 Silberschatz, Galvin and Gagne ©2013 Objectives What is an Operating System?
To describe the basic organization of computer systems
A program that acts as an intermediary between a user of a computer and the computer hardware
To provide a grand tour of the major components of operating systems
Operating system goals:
To give an overview of the many types of computing environments  Execute user programs and make solving user problems easier  Make the computer system convenient to use
To explore several open-source operating systems  Use the computer hardware in an efficient manner Operating System Concepts – 9th Edition 1.3 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition 1.4 Silberschatz, Galvin and Gagne ©2013 1  Computer System Structure Four Components of a Computer System
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 Operating System Concepts – 9th Edition 1.5 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition 1.6 Silberschatz, Galvin and Gagne ©2013 What Operating Systems Do Operating System Definition
Depends on the point of view
OS is a resource allocator
Users want convenience, ease of use  Manages all resources  Don’t care about resource utilization  Decides between conflicting requests for efficient and fair resource
But shared computer such as mainframe or minicomputer must keep all use users happy
Users of dedicate systems such as workstations have dedicated resources
OS is a control program but frequently use shared resources from servers
Handheld computers are resource poor, optimized for usability and battery  Controls execution of programs to prevent errors and improper use life of the computer
Some computers have little or no user interface, such as embedded computers in devices and automobiles Operating System Concepts – 9th Edition 1.7 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition 1.8 Silberschatz, Galvin and Gagne ©2013 2  Operating System Definition (Cont.) Computer Startup
bootstrap program is loaded at power-up or reboot
No universally accepted definition  Typically stored in ROM or EPROM, generally known as firmware  Initializes all aspects of system
“Everything a vendor ships when you order an operating system” is good approximation  Loads operating system kernel and starts execution  But varies wildly
“The one program running at all times on the computer” is the kernel. Everything else is either a system program (ships with the operating system) or an application program. Operating System Concepts – 9th Edition 1.9 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition 1.10 Silberschatz, Galvin and Gagne ©2013 Computer System Organization Computer-System Operation
Computer-system operation
I/O devices and the CPU can execute concurrently  One or more CPUs, device controllers connect through common
Each device controller is in charge of a particular device type bus providing access to shared memory  Concurrent execution of CPUs and devices competing for
Each device controller has a local buffer memory cycles
CPU moves data from/to main memory to/from local buffers
I/O is from the device to local buffer of controller
Device controller informs CPU that it has finished its operation by causing an interrupt Operating System Concepts – 9th Edition 1.11 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition 1.12 Silberschatz, Galvin and Gagne ©2013 3  Common Functions of Interrupts Interrupt Handling
Interrupt transfers control to the interrupt service routine generally,
The operating system preserves the state of the CPU by storing through the interrupt vector, which contains the addresses of all the registers and the program counter service routines
Interrupt architecture must save the address of the interrupted
Determines which type of interrupt has occurred: instruction  polling  vectored interrupt system
A trap or exception is a software-generated interrupt caused either by an error or a user request
Separate segments of code determine what action should be taken for
An operating system is interrupt driven each type of interrupt Operating System Concepts – 9th Edition 1.13 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition 1.14 Silberschatz, Galvin and Gagne ©2013 Interrupt Timeline 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 OS 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  OS indexes into I/O device table to determine device status and to modify table entry to include interrupt Operating System Concepts – 9th Edition 1.15 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition 1.16 Silberschatz, Galvin and Gagne ©2013 4  Storage Definitions and Notation Review Storage Structure
Main memory – only large storage media that the CPU can access directly The basic unit of computer storage is the bit. A bit can contain one of two values, 0  Random access and 1. All other storage in a computer is based on collections of bits. Given enough  Typically volatile bits, it is amazing how many things a computer can represent: numbers, letters, images, movies, sounds, documents, and programs, to name a few. A byte is 8
Secondary storage – extension of main memory that provides large bits, and on most computers it is the smallest convenient chunk of storage. For example, most computers don’t have an instruction to move a bit but do have one nonvolatile storage capacity to move a byte. A less common term is word, which is a given computer
Magnetic disks – rigid metal or glass platters covered with magnetic architecture’s native unit of data. A word is made up of one or more bytes. For example, a computer that has 64-bit registers and 64-bit memory addressing recording material typically has 64-bit (8-byte) words. A computer executes many operations in its native word size rather than a byte at a time.  Disk surface is logically divided into tracks, which are subdivided Computer storage, along with most computer throughput, is generally measured into sectors and manipulated in bytes and collections of bytes. A kilobyte, or KB, is 1,024 2 3 bytes; a megabyte, or MB, is 1,024 bytes; a gigabyte, or GB, is 1,024 bytes; a  The disk controller determines the logical interaction between the 4 5 terabyte, or TB, is 1,024 bytes; and a petabyte, or PB, is 1,024 bytes. device and the computer Computer manufacturers often round off these numbers and say that a megabyte is 1 million bytes and a gigabyte is 1 billion bytes. Networking measurements are an
Solid-state disks – faster than magnetic disks, nonvolatile exception to this general rule; they are given in bits (because networks move data a bit at a time).  Various technologies  Becoming more popular Operating System Concepts – 9th Edition 1.17 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition 1.18 Silberschatz, Galvin and Gagne ©2013 Storage Hierarchy Storage-Device 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
Device Driver for each device controller to manage I/O  Provides uniform interface between controller and kernel Operating System Concepts – 9th Edition 1.19 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition 1.20 Silberschatz, Galvin and Gagne ©2013 5  Caching Computer-System Architecture
Important principle, performed at many levels in a computer (in
Most systems use a single general-purpose processor hardware, operating system, software)  Most systems have special-purpose processors as well
Information in use copied from slower to faster storage temporarily
Multiprocessors systems growing in use and importance
Faster storage (cache) checked first to determine if information is  Also known as parallel systems, tightly-coupled systems there  Advantages include:  If it is, information used directly from the cache (fast) 1. Increased throughput  If not, data copied to cache and used there 2. Economy of scale 3. Increased reliability – graceful degradation or fault tolerance
Cache smaller than storage being cached  Two types:  Cache management important design problem 1. Asymmetric Multiprocessing  Cache size and replacement policy 2. Symmetric Multiprocessing Operating System Concepts – 9th Edition 1.21 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition 1.22 Silberschatz, Galvin and Gagne ©2013 How a Modern Computer Works Symmetric Multiprocessing Architecture A von Neumann architecture Operating System Concepts – 9th Edition 1.23 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition 1.24 Silberschatz, Galvin and Gagne ©2013 6  Clustered Systems Clustered Systems
Like multiprocessor systems, but multiple systems working together  Usually sharing storage via a storage-area network (SAN)  Provides a high-availability service which survives failures
Asymmetric clustering has one machine in hot-standby mode
Symmetric clustering has multiple nodes running applications, monitoring each other  Some clusters are for high-performance computing (HPC)
Applications must be written to use parallelization  Some have distributed lock manager (DLM) to avoid conflicting operations Operating System Concepts – 9th Edition 1.25 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition 1.26 Silberschatz, Galvin and Gagne ©2013 Operating System Structure Memory Layout for Multiprogrammed System
Multiprogramming needed for efficiency  Single user cannot keep CPU and I/O devices busy at all times  Multiprogramming organizes jobs (code and data) so CPU always has one to execute  A subset of total jobs in system is kept in memory  One job selected and run via job scheduling  When it has to wait (for I/O for example), OS switches to another job
Timesharing (multitasking) is logical extension in which CPU switches jobs so frequently that users can interact with each job while it is running, creating interactive computing  Response time should be < 1 second  Each user has at least one program executing in memory
process  If several jobs ready to run at the same time
CPU scheduling  If processes don’t fit in memory, swapping moves them in and out to run  Virtual memory allows execution of processes not completely in memory Operating System Concepts – 9th Edition 1.27 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition 1.28 Silberschatz, Galvin and Gagne ©2013 7  Operating-System Operations Transition from User to Kernel Mode
Interrupt driven by hardware
Timer to prevent infinite loop / process hogging resources
Software error or request creates exception or trap  Set interrupt after specific period  Division by zero, request for operating system service  Operating system decrements counter
Other process problems include infinite loop, processes modifying each other or the operating system  When counter zero generate an interrupt
Dual-mode operation allows OS to protect itself and other system components  Set up before scheduling process to regain control or terminate  User mode and kernel mode program that exceeds allotted time  Mode bit provided by hardware
Provides ability to distinguish when system is running user code or kernel code
Some instructions designated as privileged, only executable in kernel mode
System call changes mode to kernel, return from call resets it to user
Increasingly CPUs support multi-mode operations  i.e. virtual machine manager (VMM) mode for guest VMs Operating System Concepts – 9th Edition 1.29 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition 1.30 Silberschatz, Galvin and Gagne ©2013 Process Management Process Management Activities
A process is a program in execution. It is a unit of work within the The operating system is responsible for the following activities in system. Program is a passive entity, process is an active entity. connection with process management:
Process needs resources to accomplish its task  CPU, memory, I/O, files
Creating and deleting both user and system processes  Initialization data
Suspending and resuming processes
Process termination requires reclaim of any reusable resources
Providing mechanisms for process synchronization
Single-threaded process has one program counter specifying
Providing mechanisms for process communication location of next instruction to execute
Providing mechanisms for deadlock handling  Process executes instructions sequentially, one at a time, until completion
Multi-threaded process has one program counter per thread
Typically system has many processes, some user, some operating system running concurrently on one or more CPUs  Concurrency by multiplexing the CPUs among the processes / threads Operating System Concepts – 9th Edition 1.31 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition 1.32 Silberschatz, Galvin and Gagne ©2013 8  Memory Management Storage Management
All data in memory before and after processing
OS provides uniform, logical view of information storage
All instructions in memory in order to execute  Abstracts physical properties to logical storage unit - file  Each medium is controlled by device (i.e., disk drive, tape drive)
Memory management determines what is in memory when
Varying properties include access speed, capacity, data-  Optimizing CPU utilization and computer response to users transfer rate, access method (sequential or random)
Memory management activities
File-System management  Keeping track of which parts of memory are currently being used  Files usually organized into directories and by whom  Access control on most systems to determine who can access  Deciding which processes (or parts thereof) and data to move into what and out of memory  OS activities include  Allocating and deallocating memory space as needed
Creating and deleting files and directories
Primitives to manipulate files and dirs
Mapping files onto secondary storage
Backup files onto stable (non-volatile) storage media Operating System Concepts – 9th Edition 1.33 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition 1.34 Silberschatz, Galvin and Gagne ©2013 Mass-Storage Management Performance of Various Levels of Storage
Usually disks used to store data that does not fit in main memory or data that must be kept for a “long” period of time
Proper management is of central importance
Entire speed of computer operation hinges on disk subsystem and its algorithms
OS activities  Free-space management  Storage allocation  Disk scheduling
Some storage need not be fast  Tertiary storage includes optical storage, magnetic tape
Movement between levels of storage hierarchy can be explicit or  Still must be managed – by OS or applications implicit  Varies between WORM (write-once, read-many-times) and RW (read-write) Operating System Concepts – 9th Edition 1.35 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition 1.36 Silberschatz, Galvin and Gagne ©2013 9  Migration of Integer A from Disk to Register I/O Subsystem
Multitasking environments must be careful to use most recent value, no
One purpose of OS is to hide peculiarities of hardware devices from matter where it is stored in the storage hierarchy the user
I/O subsystem responsible for  Memory management of I/O including buffering (storing data temporarily while it is being transferred), caching (storing parts of data in faster storage for performance), spooling (the overlapping
Multiprocessor environment must provide cache coherency in of output of one job with input of other jobs) hardware such that all CPUs have the most recent value in their cache  General device-driver interface  Drivers for specific hardware devices
Distributed environment situation even more complex  Several copies of a datum can exist  Various solutions covered in Chapter 17 Operating System Concepts – 9th Edition 1.37 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition 1.38 Silberschatz, Galvin and Gagne ©2013 Protection and Security Computing Environments - Traditional
Protection – any mechanism for controlling access of processes or
Stand-alone general purpose machines users to resources defined by the OS
But blurred as most systems interconnect with others (i.e. the Internet)
Security – defense of the system against internal and external attacks
Portals provide web access to internal systems  Huge range, including denial-of-service, worms, viruses, identity
Network computers (thin clients) are like Web terminals theft, theft of service
Mobile computers interconnect via wireless networks
Systems generally first distinguish among users, to determine who
Networking becoming ubiquitous – even home systems use firewalls to can do what protect home computers from Internet attacks  User identities (user IDs, security IDs) include name and associated number, one per user  User ID then associated with all files, processes of that user to determine access control  Group identifier (group ID) allows set of users to be defined and controls managed, then also associated with each process, file  Privilege escalation allows user to change to effective ID with more rights Operating System Concepts – 9th Edition 1.39 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition 1.40 Silberschatz, Galvin and Gagne ©2013 10  Computing Environments - Mobile Computing Environments – Distributed
Handheld smartphones, tablets, etc
Distributed
What is the functional difference between them and a “traditional” laptop?  Collection of separate, possibly heterogeneous, systems networked
Extra feature – more OS features (GPS, gyroscope) together
Allows new types of apps like augmented reality
Network is a communications path, TCP/IP most common
Use IEEE 802.11 wireless, or cellular data networks for connectivity – Local Area Network (LAN)
Leaders are Apple iOS and Google Android – Wide Area Network (WAN) – Metropolitan Area Network (MAN) – Personal Area Network (PAN)  Network Operating System provides features between systems across network
Communication scheme allows systems to exchange messages
Illusion of a single system Operating System Concepts – 9th Edition 1.41 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition 1.42 Silberschatz, Galvin and Gagne ©2013 Computing Environments – Client-Server Computing Environments - Peer-to-Peer
Client-Server Computing
Another model of distributed system  Dumb terminals supplanted by smart PCs  Many systems now servers, responding to requests generated
P2P does not distinguish clients and servers by clients  Instead all nodes are considered peers
Compute-server system provides an interface to client to request services (i.e., database)  May each act as client, server or both
File-server system provides interface for clients to store  Node must join P2P network and retrieve files
Registers its service with central lookup service on network, or
Broadcast request for service and respond to requests for service via discovery protocol  Examples include Napster and Gnutella, Voice over IP (VoIP) such as Skype Operating System Concepts – 9th Edition 1.43 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition 1.44 Silberschatz, Galvin and Gagne ©2013 11  Computing Environments - Virtualization Computing Environments - Virtualization
Allows operating systems to run applications within other OSes
Use cases involve laptops and desktops running multiple OSes for  Vast and growing industry exploration or compatibility  Apple laptop running Mac OS X host, Windows as a guest
Emulation used when source CPU type different from target type (i.e.  Developing apps for multiple OSes without having multiple PowerPC to Intel x86) systems  Generally slowest method  QA testing applications without having multiple systems  When computer language not compiled to native code –  Executing and managing compute environments within data Interpretation centers
Virtualization – OS natively compiled for CPU, running guest OSes
VMM can run natively, in which case they are also the host also natively compiled  There is no general purpose host then (VMware ESX and Citrix  Consider VMware running WinXP guests, each running XenServer) applications, all on native WinXP host OS  VMM provides virtualization services Operating System Concepts – 9th Edition 1.45 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition 1.46 Silberschatz, Galvin and Gagne ©2013 Computing Environments - Virtualization Computing Environments – Cloud Computing
Delivers computing, storage, even apps as a service across a network
Logical extension of virtualization as based on virtualization  Amazon EC2 has thousands of servers, millions of VMs, PBs of storage available across the Internet, pay based on usage
Many types  Public cloud – available via Internet to anyone willing to pay  Private cloud – run by a company for the company’s own use  Hybrid cloud – includes both public and private cloud components  Software as a Service (SaaS) – one or more applications available via the Internet (i.e. word processor)  Platform as a Service (PaaS) – software stack ready for application use via the Internet (i.e a database server)  Infrastructure as a Service (IaaS) – servers or storage available over Internet (i.e. storage available for backup use) Operating System Concepts – 9th Edition 1.47 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition 1.48 Silberschatz, Galvin and Gagne ©2013 12  Computing Environments – Cloud Computing Computing Environments – Real-Time Embedded Systems
Cloud compute environments composed of traditional OSes, plus
Real-time embedded systems most prevalent form of computers VMMs, plus cloud management tools  Vary considerable, special purpose, limited purpose OS, real-time OS  Internet connectivity requires security like firewalls  Use expanding  Load balancers spread traffic across multiple applications
Many other special computing environments as well  Some have OSes, some perform tasks without an OS
Real-time OS has well-defined fixed time constraints  Processing must be done within constraint  Correct operation only if constraints met Operating System Concepts – 9th Edition 1.49 Silberschatz, Galvin and Gagne ©2013 Operating System Concepts – 9th Edition 1.50 Silberschatz, Galvin and Gagne ©2013 Open-Source Operating Systems
Operating systems made available in source-code format rather than just binary closed-source
Counter to the copy protection and Digital Rights Management (DRM) movement
Started by Free Software Foundation (FSF), which has “copyleft” GNU Public License (GPL)
Examples include GNU/Linux and BSD UNIX (including core of Mac OS X), and many more
Can use VMM like VMware Player (Free on Windows), Virtualbox (open source and free on many platforms - http://www.virtualbox.com)  Use to run guest operating systems for exploration Operating System Concepts – 9th Edition 1.51 Silberschatz, Galvin and Gagne ©2013 13