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Introduction Chapter 1 Agenda - Definition -Hardware concept -Software concept -The Client-Server model Definition of a Distributed System (1) A distributed system is: A collection of independent computers that appears to its users as a single coherent system.

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Chapter 1

  • -Definition
  • -Hardware concept
  • -Software concept
  • -The Client-Server model
definition of a distributed system 1
Definition of a Distributed System (1)
  • A distributed system is:
  • A collection of independent computers that appears to its users as a single coherent system.
definition of a distributed system 2
Definition of a Distributed System (2)


A distributed system organized as middleware.Note that the middleware layer extends over multiple machines.

goal of distributed system
Goal of Distributed system
  • Connecting users to resources
  • Openness
  • Transparency
  • Scalability
transparency in a distributed system
Transparency in a Distributed System

Different forms of transparency in a distributed system.

scalability problems
Scalability Problems

Examples of scalability limitations.

scaling techniques 1
Scaling Techniques (1)


  • The difference between letting:
  • a server or
  • a client check forms as they are being filled
scaling techniques 2
Scaling Techniques (2)


An example of dividing the DNS name space into zones.

hardware concepts
Hardware Concepts


Different basic organizations and memories in distributed computer systems

multiprocessors 1
Multiprocessors (1)


  • A bus-based multiprocessor.
multiprocessors 2
Multiprocessors (2)


  • A crossbar switch
  • An omega switching network
  • Lower traffic than multiprocessors
    • CPU – CPU versus CPU – Memory traffic
  • Homogeneous or Heterogeneous
  • Each node is an autonomous machine
    • Private memory

Homogeneous Multicomputer Systems (1)

  • Homogeneous access to network
    • Single network
  • Bus-based or point-to-point communication
  • Similar nodes
    • Same processors and memory space
heterogeneous multicomputers
Heterogeneous Multicomputers
  • None-homogeneous access to network
    • Different network
  • Distributed systems are commonly built on this H/W category
    • Need S/W to make it transparent
  • Different nodes
    • Nodes can be complex system
software concepts
Software Concepts
  • An overview between
  • DOS (Distributed Operating Systems)
  • NOS (Network Operating Systems)
  • Middleware
uniprocessor operating systems
Uniprocessor Operating Systems


  • Separating applications from operating system code through a microkernel.
multicomputer operating systems 1
Multicomputer Operating Systems (1)


  • General structure of a multicomputer operating system
multicomputer operating systems 2
Multicomputer Operating Systems (2)


  • Alternatives for blocking and buffering in message passing.
distributed shared memory systems 1
Distributed Shared Memory Systems (1)
  • Pages of address space distributed among four machines
  • Situation after CPU 1 references page 10
  • Situation if page 10 is read only and replication is used
distributed shared memory systems 2
Distributed Shared Memory Systems (2)


  • False sharing of a page between two independent processes.
network operating system 1
Network Operating System (1)


  • General structure of a network operating system.
network operating system 2
Network Operating System (2)


  • Two clients and a server in a network operating system.
network operating system 3
Network Operating System (3)


  • Different clients may mount the servers in different places.
dos and nos v s ds
DOS and NOS v.s DS
  • NOS qualifies as DS?
    • No single coherent view
    • Scalable and open
  • DOS qualifies as DS?
    • Computers are not independent
    • Easy to use and transparent
positioning middleware
Positioning Middleware


  • General structure of a distributed system as middleware.
middleware and openness
Middleware and Openness


  • In an open middleware-based distributed system, the protocols used by each middleware layer should be the same, as well as the interfaces they offer to applications.
comparison between systems
Comparison between Systems
  • A comparison between multiprocessor operating systems, multicomputer operating systems, network operating systems, and middleware based distributed systems.
client and server
Client and Server

General interaction between a client and a server.

  • -Clients request services.
  • -Servers provide services by replying to the requests.
an example client and server 1
An Example Client and Server (1)
  • The header.h file used by the client and server.
  • Client and server need to agree on a couple things first!
an example client and server 2
An Example Client and Server (2)
  • A sample server (A basic server loop)
  • -The server continually listens for new requests (receive).
  • -Extracting the request and simply executes it.
  • -It then prepares a response message and sends it back to the requesting client.
an example client and server 3
An Example Client and Server (3)

1-27 b

  • Sample Client: using the server to copy a file.
application layering
Application Layering
  • A client-server application typically consists of three layers:
  • 1.User-Interface level:
  • +Consists of the programs that allow end users to interact with application.
  • 2.Processing level:
  • +Implements the application logic (core functionality)
  • +Typically implemented at the server side
  • 3.Data level
  • +Maintain the actual data on which the application operate.
  • +Also keep data consistent across different application
application layering36

Web browser




Database server

Application Layering
  • The general organization of an Internet search engine into three different layers
client server architectures
Client-Server Architectures

Two-tiers Architectures


  • Alternative client-server organizations (a) – (e).
client server architectures con t
Client-Server Architectures (con.t)

Three-tiers Architectures


  • An example of a server acting as a client.
modern architectures
Modern Architectures

-Vertical distribution Model : where the tiers corresponded directly with the logical organization of the apps (The previous architectures)

-Horizontaldistribution Model: where the application layers are physically split up into logically equivalent part

-> This is how high-performance web services (e.g., Google, Amazon, E-bay..)

  • An example of horizontal distribution of a Web service.