Chapter 1: Introduction PDF

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 Kernel Da...

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 Kernel Data Structures Computing Environments Open-Source Operating Systems 1.2  Objectives To describe the basic organization of computer systems To provide a grand tour of the major components of operating systems To give an overview of the many types of computing environments To explore several open-source operating systems 1.3  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 1.4  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 1.5 Four Components of a Computer System 1.6  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 1.7  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 1.8  Operating System Definition (Cont.) No universally accepted definition “Everything a vendor ships when you order an operating system” is a good approximation  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. 1.9  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 1.10  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 1.11  Computer-System Operation I/O devices and the CPU can execute concurrently Each device controller is in charge of a particular device type Each device controller has a local buffer 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 1.12  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 A trap or exception is a software-generated interrupt caused either by an error or a user request An operating system is interrupt driven 1.13  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 1.14 Interrupt Timeline 1.15  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 1.16  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 1.17  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 1.18 Storage-Device Hierarchy 1.19  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 1.20  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 1.21 How a Modern Computer Works A von Neumann architecture 1.22  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 1.23 Symmetric Multiprocessing Architecture 1.24  A Dual-Core Design Multi-chip and multicore Systems containing all chips  Chassis containing multiple separate systems 1.25  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 1.26 Clustered Systems 1.27  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 1.28 Memory Layout for Multiprogrammed System 1.29  Operating-System Operations Interrupt driven (hardware and software)  Hardware interrupt by one of the devices  Software interrupt (exception or trap):  Software error (e.g., division by zero)  Request for operating system service  Other process problems include infinite loop, processes modifying each other or the operating system 1.30  Operating-System Operations (cont.) Dual-mode operation allows OS to protect itself and other system components  User mode and kernel mode  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 1.31  Transition from User to Kernel Mode Timer to prevent infinite loop / process hogging resources  Timer is set to interrupt the computer after some time period  Keep a counter that is decremented by the physical clock.  Operating system set the counter (privileged instruction)  When counter zero generate an interrupt  Set up before scheduling process to regain control or terminate program that exceeds allotted time 1.32  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 1.33  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 1.34  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 1.35  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 1.36  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 1.37  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 1.38  Computing Environments - Virtualization Use cases involve laptops and desktops running multiple OSes for exploration or compatibility  Apple laptop running Mac OS X host, Windows as a guest  Developing apps for multiple OSes without having multiple systems  QA testing applications without having multiple systems  Executing and managing compute environments within data centers VMM can run natively, in which case they are also the host  There is no general purpose host then (VMware ESX and Citrix XenServer) 1.39 Computing Environments - Virtualization 1.40  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) 1.41  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 1.42  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 1.43  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 1.44