A5_DistSysCh1 - Distributed Systems Tanenbaum Chapter 1...

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Unformatted text preview: Distributed Systems Tanenbaum Chapter 1 Outline Definition of a Distributed System Goals of a Distributed System Types of Distributed Systems What Is A Distributed System? A collection of independent computers that appears to its users as a single coherent system. Features: No shared memory message-based communication Each runs its own local OS Heterogeneity Ideal: to present a single-system image: The distributed system looks like a single computer rather than a collection of separate computers. Distributed System Characteristics To present a single-system image: Hide internal organization, communication details Provide uniform interface Easily expandable Adding new computers is hidden Continuous availability Failures in one component can be covered by other components Supported by middleware Definition of a Distributed System Figure 1-1 . A distributed system organized as middleware. The middleware layer runs on all machines, and offers a uniform interface to the system Middleware Examples CORBA (Common Object Request Broker Architecture) DCOM (Distributed Component Object Management) being replaced by .net Suns ONC RPC (Remote Procedure Call) RMI (Remote Method Invocation) SOAP (Simple Object Access Protocol) Middleware Examples All of the previous examples support communication across a network: They provide protocols that allow a program running on one kind of computer, using one kind of operating system, to call a program running on another computer with a different operating system The communicating programs must be running the same middleware. Distributed System Goals Resource Accessibility Distribution Transparency Openness Scalability Goal 1 Resource Availability Support user access to remote resources (printers, data files, web pages, CPU cycles) and the fair sharing of the resources Economics of sharing expensive resources Performance enhancement due to multiple processors; also due to ease of collaboration and info exchange Groupware: tools to support collaboration Resource sharing introduces security problems. Goal 2 Distribution Transparency Software hides some of the details of the distribution of system resources. Makes the system more user friendly. A distributed system that appears to its users & applications to be a single computer system is said to be transparent . Users & apps should be able to access remote resources in the same way they access local resources. Transparency has several dimensions. Types of Transparency Transparency Description Access Hide differences in data representation & resource access (enables interoperability) Location Hide location of resource (can use resource without knowing its location) Migration Hide possibility that a system may change location of resource (no effect on access)...
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This note was uploaded on 12/14/2011 for the course CS 690 taught by Professor Staff during the Fall '11 term at University of Alabama - Huntsville.

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A5_DistSysCh1 - Distributed Systems Tanenbaum Chapter 1...

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