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UMass Amherst CS 677 - Distributed Operating Systems

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1CS677: Distributed OSComputer ScienceLecture 1, page 1Distributed Operating SystemsSpring 2003Prashant ShenoyUMass Computer Sciencehttp://lass.cs.umass.edu/~shenoy/courses/677CS677: Distributed OSComputer ScienceLecture 1, page 2Course Syllabus• CMPSCI 677: Distributed Operating Systems• Instructor: Prashant Shenoy– Email: [email protected], Phone: (413) 577 0850– Office hours: Tuesday 12:30-1:30, CS 336, or by appt• Teaching Asst: Gary Holness– Email: [email protected], Phone: (413) 545 3039– Office hours: TBA, CS 311, (413) 577-6310• Course web page: http://lass.cs.umass.edu/~shenoy/courses/6772CS677: Distributed OSComputer ScienceLecture 1, page 3Course Outline • Introduction (today)– What, why, why not?– Basics• Interprocess Communication– RPCs, RMI, message- and stream-oriented communication• Processes and their scheduling– Thread/process scheduling, code/process migration• Naming and location management– Entities, addresses, access pointsCS677: Distributed OSComputer ScienceLecture 1, page 4Course Outline• Canonical problems and solutions– Mutual exclusion, leader election, clock synchronization, …• Resource sharing, replication and consistency– DSM, DFS, consistency issues, caching and replication• Fault-tolerance• Security in distributed Systems• Distributed middleware• Advanced topics: web, multimedia, real-time and mobile systems3CS677: Distributed OSComputer ScienceLecture 1, page 5Misc. Course Details • Textbook: Distributed Systems by Tannenbaum and Van Steen, Prentice Hall 2001• Grading– 4-5 Homeworks (20%), 3-4 programming assignments (35%)– 1 mid-term and 1 final (40%), class participation (5%)• Course mailing list: [email protected]– You need to add yourself to this list! [ see class web page ]• Pre-requisites– Undergrad course in operating systems– Good programming skills in a high-level prog. languageCS677: Distributed OSComputer ScienceLecture 1, page 6Definition of a Distributed System • A distributed system:– Multiple connected CPUs working together– A collection of independent computers that appears to its users as a single coherent system• Examples: parallel machines, networked machines4CS677: Distributed OSComputer ScienceLecture 1, page 7Advantages and Disadvantages• Advantages– Communication and resource sharing possible– Economics – price-performance ratio– Reliability, scalability– Potential for incremental growth• Disadvantages– Distribution-aware PLs, OSs and applications– Network connectivity essential– Security and privacyCS677: Distributed OSComputer ScienceLecture 1, page 8Transparency in a Distributed SystemDifferent forms of transparency in a distributed system.Hide whether a (software) resource is in memory or on diskPersistenceHide the failure and recovery of a resourceFailureHide that a resource may be shared by several competitive usersConcurrencyHide that a resource may be shared by several competitive usersReplicationHide that a resource may be moved to another location while in useRelocationHide that a resource may move to another locationMigration Hide where a resource is locatedLocationHide differences in data representation and how a resource is accessedAccessDescriptionTransparency5CS677: Distributed OSComputer ScienceLecture 1, page 9Scalability ProblemsExamples of scalability limitations.Doing routing based on complete informationCentralized algorithmsA single on-line telephone bookCentralized dataA single server for all usersCentralized servicesExampleConceptCS677: Distributed OSComputer ScienceLecture 1, page 10Hardware Concepts: Multiprocessors (1)• Multiprocessor dimensions– Memory: could be shared or be private to each CPU– Interconnect: could be shared (bus-based) or switched• A bus-based multiprocessor.6CS677: Distributed OSComputer ScienceLecture 1, page 11Multiprocessors (2)a) A crossbar switch b) An omega switching network1.8CS677: Distributed OSComputer ScienceLecture 1, page 12Homogeneous Multicomputer Systemsa) Grid b) Hypercube1-97CS677: Distributed OSComputer ScienceLecture 1, page 13Distributed Systems Models• Minicomputer model (e.g., early networks)– Each user has local machine– Local processing but can fetch remote data (files, databases)• Workstation model (e.g., Sprite)– Processing can also migrate• Client-server Model (e.g., V system, world wide web)– User has local workstation– Powerful workstations serve as servers (file, print, DB servers)• Processor pool model (e.g., Amoeba, Plan 9)– Terminals are Xterms or diskless terminals– Pool of backend processors handle processingCS677: Distributed OSComputer ScienceLecture 1, page 14Uniprocessor Operating Systems• An OS acts as a resource manager or an arbitrator– Manages CPU, I/O devices, memory• OS provides a virtual interface that is easier to use than hardware• Structure of uniprocessor operating systems– Monolithic (e.g., MS-DOS, early UNIX)• One large kernel that handles everything– Layered design• Functionality is decomposed into N layers• Each layer uses services of layer N-1 and implements new service(s) for layer N+18CS677: Distributed OSComputer ScienceLecture 1, page 15Uniprocessor Operating SystemsMicrokernel architecture• Small kernel• user-level servers implement additional functionality CS677: Distributed OSComputer ScienceLecture 1, page 16Distributed Operating System• Manages resources in a distributed system– Seamlessly and transparently to the user• Looks to the user like a centralized OS– But operates on multiple independent CPUs• Provides transparency– Location, migration, concurrency, replication,…• Presents users with a virtual uniprocessor9CS677: Distributed OSComputer ScienceLecture 1, page 17Types of Distributed OSsProvide distribution transparencyAdditional layer atop of NOS implementing general-purpose servicesMiddlewareOffer local services to remote clientsLoosely-coupled operating system for heterogeneous multicomputers (LAN and WAN)NOSHide and manage hardware resourcesTightly-coupled operating system for multi-processors and homogeneous multicomputersDOSMain GoalDescriptionSystemCS677: Distributed OSComputer ScienceLecture 1, page 18Multiprocessor Operating Systems • Like a uniprocessor operating system • Manages multiple CPUs transparently to the user• Each processor has its own hardware cache– Maintain consistency of cached


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