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Introduction Chapter 1 Part II Hardware and Software Concepts Hardware Concepts (1) A DS = machines connected together How are these machines connected together? Review: multiple-CPU computer Characterization Hardware Concepts (2) 1.6

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Introduction l.jpg

Introduction

Chapter 1

Part II

Hardware and Software Concepts


Hardware concepts 1 l.jpg
Hardware Concepts (1)

  • A DS = machines connected together

  • How are these machines connected together?

  • Review: multiple-CPU computer Characterization


Hardware concepts 2 l.jpg
Hardware Concepts (2)

1.6

Different basic organizations and memories in distributed computer systems


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Multiprocessors (1)

Single

Address

Space

Similar

CPUs

Direct, uniform

Access to memory

A bus-based multiprocessor

1.7

  • Traffic Problems

  • Caching (hit ratio, consistency)

  • Scalable?


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Multiprocessors (2)

1.8

  • A crossbar switch

  • An omega switching network


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Multicomputers

  • Each node is an autonomous machine

    • Private memory

  • Lower traffic than multiprocessors

    • CPU-CPU versus CPU-Memory traffic

  • Homogeneous or Heterogeneous


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Homogeneous Multicomputers (1)

  • Similar nodes

    • Same processors and memory space

  • Homogeneous access to network

    • Single network

  • Bus-based or point-to-point communication


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Homogeneous Multicomputers (2)

1-9

  • Grid

  • Hypercube


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Heterogeneous Multicomputers

  • Different nodes

    • Nodes can be complex systems

  • Non-homogeneous access to network

    • Different networks

  • DS are commonly built on this hardware category

    • Need software to make it transparent


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Software Concepts

  • A DS is similar to an OS

    • Resource management

    • Virtual machine

  • OS =

    • Tightly coupled

    • Loosely coupled


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Uniprocessor Operating Systems

1.11

  • Separating applications from operating system code through a microkernel.


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Multiple CPU Operating Systems

  • An overview between

  • DOS (Distributed Operating Systems)

  • NOS (Network Operating Systems)

  • Middleware


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Multiprocessor OS (1)

  • Similar to uniprocessor

  • Single ready queue

  • Mutual exclusion through monitors and semaphores

  • Multiple CPUs


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Multiprocessor DOS (1)

Ready queue

Single Ready Queue


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Multiprocessor DOS (2)

CPU

CPU

CPU

Kernel


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Multiprocessor DOS (3)

  • A blocks or time-quantum expires

  • CPU 1 runs the scheduler and chooses D

A (W|R)

A (X)

  • Schedule A again on which CPU??

B (X)

C (X)

D (X)

D (R)

E (R)

C

B

D

A

OS


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Java Monitors (1)

public class Counter {

private int count = 0;

public synchronized void reset() { count = 0;}

public synchronized int value() { return count;}

public synchronized void inc() { count = count + 1;}

public synchronized void dec() { count = count – 1;}

}

  • A monitor to protect an integer against concurrent access.


Java monitors 2 l.jpg
Java Monitors (2)

Java Compiler

Lock object

Counter

Object

public synchronized void reset() { count = 0;}

public synchronized void reset() {

acquire(this.lock);

count = 0;

release(this.lock)

}


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Multicomputer DOS (1)

1.14

  • General structure of a multicomputer operating system


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Multicomputer DOS (2)

1.15

  • Alternatives for blocking and buffering in message passing.


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Multicomputer DOS (3)

  • Relation between blocking, buffering, and reliable communications.


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Distributed-Shared Memory

  • Multicomputers are harder to program

  • Multiprocessors are easier to program

  • Multicomputers are more efficient and better scalable than multiprocessors

  • DSM offers a reconciliation


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Page-Based DSM Example (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


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Page-Based DSM Example (2)

X

Y

1.18

  • False sharing of a page between two independent processes.


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Network OS (1)

  • Hardware is not homogeneous

  • More primitive than DS

    • Not fully transparent


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Network OS (2)

1-19

  • General structure of a network operating system.


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Network OS (3)

  • Services:

    • rlogin

    • File transfer

  • This led to the client/server organization


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Network OS (4)

1-20

  • Two clients and a server in a network operating system.


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Network OS (5)

1.21

  • Different clients may mount the servers in different places.


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DOS and NOS versus DS (1)

  • DOS qualifies as DS?

    • Computers are not independent

    • Easy to use and transparent

  • NOS qualifies as DS?

    • No single coherent view

    • Scalable and open


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Positioning Middleware

1-22

  • General structure of a distributed system as middleware.


Middleware l.jpg
Middleware

  • Local system provides:

    • Local resource management

    • Communication mechanism

  • Middleware does not manage the local nodes

  • Middleware hides heterogeneity

    • Should not call local services directly


Middleware types l.jpg
Middleware Types

  • File-based (NOS + Transparency)

    • For traditional files only

  • RPC-based

    • Hides communication

  • Object-based

    • Remote Method Invocation

  • Document-based

    • The Web


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Middleware Services

  • Communication Facilities

  • Naming

  • Persistence

  • Distributed Transactions

  • Security


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Middleware and Openness

1.23

  • 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.


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Comparison between Systems

Very High

High

Low

High

No

Yes

No

Yes

N

N

1

N

Shared

memory

Messages

Files

Model specific

Global,

distributed

Per node

Global,

Central

Per node

Yes

Varies

Moderately

No

Closed

Closed

Open

Open

  • A comparison between multiprocessor operating systems, multicomputer operating systems, network operating systems, and middleware based distributed systems.


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