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Chapter 1: Introduction Operating System Concepts – 9th Edit9on Silberschatz, Galvin and Gagne ©2013  Computer System Structure Computer system can be divided into four components: Hardware – provides basic computing resources...

Chapter 1: Introduction Operating System Concepts – 9th Edit9on Silberschatz, Galvin and Gagne ©2013  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 Operating System Concepts – 9th Edition 1.2 Silberschatz, Galvin and Gagne ©2013  Four Components of a Computer System Operating System Concepts – 9th Edition 1.3 Silberschatz, Galvin and Gagne ©2013  What Operating Systems Do Depends on the point of view Users want convenience, ease of use and good performance 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 Concepts – 9th Edition 1.4 Silberschatz, Galvin and Gagne ©2013  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 Operating System Concepts – 9th Edition 1.5 Silberschatz, Galvin and Gagne ©2013  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 Operating System Concepts – 9th Edition 1.6 Silberschatz, Galvin and Gagne ©2013  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 Operating System Concepts – 9th Edition 1.7 Silberschatz, Galvin and Gagne ©2013  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 1.8 Silberschatz, Galvin and Gagne ©2013  Storage Definitions and Notation Review The basic unit of computer storage is the bit. A bit can contain one of two values, 0 and 1. All other storage in a computer is based on collections of bits. Given enough 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 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 to move a byte. A less common term is word, which is a given computer 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 typically has 64-bit (8-byte) words. A computer executes many operations in its native word size rather than a byte at a time. Computer storage, along with most computer throughput, is generally measured and manipulated in bytes and collections of bytes. A kilobyte, or KB, is 1,024 bytes a megabyte, or MB, is 1,0242 bytes a gigabyte, or GB, is 1,0243 bytes a terabyte, or TB, is 1,0244 bytes a petabyte, or PB, is 1,0245 bytes 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 exception to this general rule; they are given in bits (because networks move data a bit at a time). Operating System Concepts – 9th Edition 1.9 Silberschatz, Galvin and Gagne ©2013  Storage Structure Main memory – only large storage media that the CPU can access directly Random access Typically volatile Secondary storage – extension of main memory that provides large nonvolatile storage capacity Hard disks – rigid metal or glass platters covered with magnetic recording material Disk surface is logically divided into tracks, which are subdivided into sectors The disk controller determines the logical interaction between the device and the computer Solid-state disks – faster than hard disks, nonvolatile Various technologies Becoming more popular Operating System Concepts – 9th Edition 1.10 Silberschatz, Galvin and Gagne ©2013  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 Device Driver for each device controller to manage I/O Provides uniform interface between controller and kernel Operating System Concepts – 9th Edition 1.11 Silberschatz, Galvin and Gagne ©2013  Storage-Device Hierarchy Operating System Concepts – 9th Edition 1.12 Silberschatz, Galvin and Gagne ©2013  Caching Important principle, performed at many levels in a computer (in hardware, operating system, software) Information in use copied from slower to faster storage temporarily Faster storage (cache) checked first to determine if information is there If it is, information used directly from the cache (fast) If not, data copied to cache and used there Cache smaller than storage being cached Cache management important design problem Cache size and replacement policy Operating System Concepts – 9th Edition 1.13 Silberschatz, Galvin and Gagne ©2013  How a Modern Computer Works A von Neumann architecture Operating System Concepts – 9th Edition 1.14 Silberschatz, Galvin and Gagne ©2013  Computer-System Architecture Most systems use a single general-purpose processor Most systems have special-purpose processors as well Multiprocessors systems growing in use and importance Also known as parallel systems, tightly-coupled systems Advantages include: 1. Increased throughput 2. Economy of scale 3. Increased reliability – graceful degradation or fault tolerance Two types: 1. Asymmetric Multiprocessing – each processor is assigned a specie task. 2. Symmetric Multiprocessing – each processor performs all tasks Operating System Concepts – 9th Edition 1.15 Silberschatz, Galvin and Gagne ©2013  Symmetric Multiprocessing Architecture Operating System Concepts – 9th Edition 1.16 Silberschatz, Galvin and Gagne ©2013  A Dual-Core Design Multi-chip and multicore Systems containing all chips Chassis containing multiple separate systems Operating System Concepts – 9th Edition 1.17 Silberschatz, Galvin and Gagne ©2013  Operating System Structure Multiprogramming (Batch system) 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 1.18 Silberschatz, Galvin and Gagne ©2013  Memory Layout for Multiprogrammed System Operating System Concepts – 9th Edition 1.19 Silberschatz, Galvin and Gagne ©2013  Process Management A process is a program in execution. It is a unit of work within the system. Program is a passive entity, process is an active entity. Process needs resources to accomplish its task CPU, memory, I/O, files Initialization data Process termination requires reclaim of any reusable resources Single-threaded process has one program counter specifying location of next instruction to execute 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 1.20 Silberschatz, Galvin and Gagne ©2013  Process Management Activities The operating system is responsible for the following activities in connection with process management: Creating and deleting both user and system processes Suspending and resuming processes Providing mechanisms for process synchronization Providing mechanisms for process communication Providing mechanisms for deadlock handling Operating System Concepts – 9th Edition 1.21 Silberschatz, Galvin and Gagne ©2013  Memory Management To execute a program all (or part) of the instructions must be in memory All (or part) of the data that is needed by the program must be in memory. Memory management determines what is in memory and when Optimizing CPU utilization and computer response to users Memory management activities Keeping track of which parts of memory are currently being used and by whom Deciding which processes (or parts thereof) and data to move into and out of memory Allocating and deallocating memory space as needed Operating System Concepts – 9th Edition 1.22 Silberschatz, Galvin and Gagne ©2013  Storage Management OS provides uniform, logical view of information storage Abstracts physical properties to logical storage unit - file Each medium is controlled by device (i.e., disk drive, tape drive)  Varying properties include access speed, capacity, data- transfer rate, access method (sequential or random) File-System management Files usually organized into directories Access control on most systems to determine who can access what OS activities include  Creating and deleting files and directories  Primitives to manipulate files and directories  Mapping files onto secondary storage  Backup files onto stable (non-volatile) storage media Operating System Concepts – 9th Edition 1.23 Silberschatz, Galvin and Gagne ©2013  Mass-Storage Management 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 Still must be managed – by OS or applications Varies between WORM (write-once, read-many-times) and RW (read-write) Operating System Concepts – 9th Edition 1.24 Silberschatz, Galvin and Gagne ©2013  Migration of data “A” from Disk to Register Multitasking environments must be careful to use most recent value, no matter where it is stored in the storage hierarchy Multiprocessor environment must provide cache coherency in hardware such that all CPUs have the most recent value in their cache Distributed environment situation even more complex Several copies of a datum can exist Various solutions covered in Chapter 17 Operating System Concepts – 9th Edition 1.25 Silberschatz, Galvin and Gagne ©2013  Protection and Security Protection – any mechanism for controlling access of processes or users to resources defined by the OS Security – defense of the system against internal and external attacks Huge range, including denial-of-service, worms, viruses, identity theft, theft of service Systems generally first distinguish among users, to determine who can do what 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 1.26 Silberschatz, Galvin and Gagne ©2013  Computing Environments - Traditional Stand-alone general purpose machines But blurred as most systems interconnect with others (i.e., the Internet) Portals provide web access to internal systems Network computers (thin clients) are like Web terminals Mobile computers interconnect via wireless networks Networking becoming ubiquitous – even home systems use firewalls to protect home computers from Internet attacks Operating System Concepts – 9th Edition 1.27 Silberschatz, Galvin and Gagne ©2013  Computing Environments - Mobile Handheld smartphones, tablets, etc What is the functional difference between them and a “traditional” laptop? Extra feature – more OS features (GPS, gyroscope) Allows new types of apps like augmented reality Use IEEE 802.11 wireless, or cellular data networks for connectivity Leaders are Apple iOS and Google Android Operating System Concepts – 9th Edition 1.28 Silberschatz, Galvin and Gagne ©2013  Computing Environments – Distributed Distributed computiing Collection of separate, possibly heterogeneous, systems networked together  Network is a communications path, TCP/IP most common – Local Area Network (LAN) – 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 1.29 Silberschatz, Galvin and Gagne ©2013  Computing Environments – Client-Server Client-Server Computing Dumb terminals supplanted by smart PCs Many systems now servers, responding to requests generated by clients  Compute-server system provides an interface to client to request services (i.e., database)  File-server system provides interface for clients to store and retrieve files Operating System Concepts – 9th Edition 1.30 Silberschatz, Galvin and Gagne ©2013  Computing Environments - Peer-to-Peer Another model of distributed system P2P does not distinguish clients and servers Instead all nodes are considered peers May each act as client, server or both Node must join P2P network  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 1.31 Silberschatz, Galvin and Gagne ©2013  Computing Environments - Virtualization Allows operating systems to run applications within other OSes Vast and growing industry Emulation used when source CPU type different from target type (i.e. PowerPC to Intel x86) Generally slowest method When computer language not compiled to native code – Interpretation Virtualization – OS natively compiled for CPU, running guest OSes also natively compiled Consider VMware running WinXP guests, each running applications, all on native WinXP host OS VMM (virtual machine Manager) provides virtualization services Operating System Concepts – 9th Edition 1.32 Silberschatz, Galvin and Gagne ©2013  Computing Environments - Virtualization Operating System Concepts – 9th Edition 1.33 Silberschatz, Galvin and Gagne ©2013  Computing Environments – Cloud Computing Delivers computing, storage, even apps as a service across a network Logical extension of virtualization because it uses virtualization as the base for it functionality. Amazon EC2 has thousands of servers, millions of virtual machines, petabytes 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 1.34 Silberschatz, Galvin and Gagne ©2013  Computing Environments – Cloud Computing Cloud computing environments composed of traditional OSes, plus VMMs, plus cloud management tools Internet connectivity requires security like firewalls Load balancers spread traffic across multiple applications Operating System Concepts – 9th Edition 1.35 Silberschatz, Galvin and Gagne ©2013  Computing Environments – Real-Time Embedded Systems Real-time embedded systems most prevalent form of computers Vary considerable, special purpose, limited purpose OS, real-time OS Use expanding 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 1.36 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 1.37 Silberschatz, Galvin and Gagne ©2013  End of Chapter 1 Operating System Concepts – 9th Edit9on Silberschatz, Galvin and Gagne ©2013