Introduction - Introduction to Computer Science - Lecture Slides, Slides of Computer Science

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Introduction Docsity.com 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 Docsity.com 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 Docsity.com Four Components of a Computer System user user user user 1 2 3 n compiler assembler text editor database system system and application programs operating system computer hardware Docsity.com 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 Docsity.com 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 Docsity.com 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 Docsity.com 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 Docsity.com 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 Docsity.com 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 Docsity.com Storage Structure • Main memory – only large storage media that the CPU can access directly • Secondary storage – extension of main memory that provides large nonvolatile storage capacity • Magnetic 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 Docsity.com 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 Docsity.com Computer-System Architecture • Most systems use a single general-purpose processor (PDAs through mainframes) – 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 2. Symmetric Multiprocessing Docsity.com How a Modern Computer Works ; thread of execution eyoro — instruction execution —> cycle «— data movement —~ jsenbs! of, —— ydnusequ] ——> DMA instructions and data memory Docsity.com 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 Docsity.com Operating System Structure • 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 Docsity.com Memory Layout for Multiprogrammed System 512M operating system job 1 job 2 job 3 job 4 Docsity.com 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 Docsity.com 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 Docsity.com Memory Management • All data in memory before and after processing • All instructions in memory in order to execute • Memory management determines what is in memory 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 Docsity.com Performance of Various Levels of Storage • Movement between levels of storage hierarchy can be explicit or implicit Docsity.com Migration of Integer 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 Docsity.com I/O Subsystem • One purpose of OS is to hide peculiarities of hardware devices from 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 of output of one job with input of other jobs) – General device-driver interface – Drivers for specific hardware devices Docsity.com Computing Environments (Cont)  Client-Server Computing  Dumb terminals supplanted by smart PCs  Many systems now servers, responding to requests generated by clients  Compute-server provides an interface to client to request services (i.e. database)  File-server provides interface for clients to store and retrieve files Docsity.com Peer-to-Peer Computing • 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 Docsity.com Web-Based Computing • Web has become ubiquitous • PCs most prevalent devices • More devices becoming networked to allow web access • New category of devices to manage web traffic among similar servers: load balancers • Use of operating systems like Windows 95, client-side, have evolved into Linux and Windows XP, which can be clients and servers Docsity.com