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    UNIT 6 Hardware & Software Concepts PDF

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    Distributed Systems: hardware and Software Concepts - (c) 2004-2006 g.p. Picco. Distributed Systems are based on multiprocessors, heterogeneous multicomputers, Parallel computing vs. Distributed computing. A Distributed Operating System (dos) hides the complexity of distribution behind a well-designed programming model.

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    UNIT 6 Hardware & Software Concepts PDF

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    Distributed Systems: hardware and Software Concepts - (c) 2004-2006 g.p. Picco. Distributed Systems are based on multiprocessors, heterogeneous multicomputers, Parallel computing vs. Distributed computing. A Distributed Operating System (dos) hides the complexity of distribution behind a well-designed programming model.

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    Distributed Systems: hardware and Software Concepts - (c) 2004-2006 g.p. Picco. Distributed Systems are based on multiprocessors, heterogeneous multicomputers, Parallel computing vs. Distributed computing. A Distributed Operating System (dos) hides the complexity of distribution behind a well-designed programming model.

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    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    1K views9 pages

    UNIT 6 Hardware & Software Concepts PDF

    Uploaded by

    lavanyatumu
    Distributed Systems: hardware and Software Concepts - (c) 2004-2006 g.p. Picco. Distributed Systems are based on multiprocessors, heterogeneous multicomputers, Parallel computing vs. Distributed computing. A Distributed Operating System (dos) hides the complexity of distribution behind a well-designed programming model.

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    of 9

    Distributed Systems:

    Hardware and Software Concepts


    Gian Pietro Picco
    Dipartimento di Elettronica e Informazione
    Politecnico di Milano, Italy
    picco@elet.polimi.it
    http://www.elet.polimi.it/~picco

    P olitecnico
    di M ilano

    Distributed Hardware

    Multiprocessors vs. multicomputers


    Homogeneous vs. heterogeneous (multicomputers)
    Parallel computing vs. distributed computing
    Distributed Systems - 2004-2006 G.P. Picco

    P olitecnico
    di M ilano

    Classes of Distributed Systems


    System

    Description

    Main Goal

    Distributed OS

    Tightly-coupled operating system for multiprocessors and homogeneous multicomputers

    Hide and manage


    hardware resources

    Network OS

    Loosely-coupled operating system for


    heterogeneous multicomputers (LAN and WAN)

    Offer local services


    to remote clients

    Middleware

    Additional layer atop of NOS implementing generalpurpose services

    Provide distribution
    transparency

    All provide support for the development of distributed


    applications
    The first two also provide services directly to users
    Distributed Systems - 2004-2006 G.P. Picco

    P olitecnico
    di M ilano

    Distributed Operating System

    Multiprocessor vs. multicomputer


    No physical shared memory: only message passing
    Different semantics, different reliability assumptions
    Distributed Systems - 2004-2006 G.P. Picco

    P olitecnico
    di M ilano

    Distributed Shared Memory


    Powerful abstraction
    for programmers
    Nothing changes w.r.t.
    centralized models
    No need for message
    passing

    Optimized using
    replication, to
    increase availability
    Efficiency problems
    False sharing

    Distributed Systems - 2004-2006 G.P. Picco

    P olitecnico
    di M ilano

    Network Operating System

    BSD sockets, NFS are examples of services


    At the core of the client-server paradigm
    Distributed Systems - 2004-2006 G.P. Picco

    P olitecnico
    di M ilano

    Network Operating System

    Users may have both explicit access to remote


    resources (e.g., through scp, ssh) and implicit access
    (e.g., through mounted file systems)
    Inconsistent views across the system

    Heterogeneity and independency of host:


    Cons: difficult to manage and to use
    Pro: more scalable

    Programming abstraction are very low-level


    Distributed Systems - 2004-2006 G.P. Picco

    P olitecnico
    di M ilano

    Middleware

    Hides the complexity of distribution behind a well-designed


    programming model
    Examples: CORBA, RMI, publish-subscribe, TP monitors,
    Discussed in detail during the course

    Distributed Systems - 2004-2006 G.P. Picco

    P olitecnico
    di M ilano

    Comparison
    Distributed OS
    Item

    Network OS

    Middleware

    Multiprocessor

    Multicomputer

    Degree of transparency

    Very High

    High

    Low

    High

    Same OS on all nodes

    Yes

    Yes

    No

    No

    Number of copies of OS

    Basis for communication

    Shared memory

    Messages

    Files

    Model specific

    Resource management

    Global, central

    Global,
    distributed

    Per node

    Per node

    Scalability

    None

    Moderate

    High

    Varies

    Openness

    Closed

    Closed

    Open

    Open

    Distributed Systems - 2004-2006 G.P. Picco

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