Introduction

Dr. Ying Lu

ylu@cse.unl.edu

CSCE455/855 Distributed Operating Systems

Most of the lecture notes are from the textbook companion website

Some of the lecture notes are based on slides created by Dr. Zahorjan at Univ. of Washington and Dr. Konev at Univ. of Liverpool

I have modified them and added new slides

Giving credit where credit is due:

CSCE455/855 Distributed Operating Systems

What is an Operating System?

The text: “an intermediary between the user of a computer

and the computer hardware” “manages the computer hardware” “an amazing aspect of operating systems is how

varied they are in accomplishing these tasks … mainframe operating systems … personal computer operating systems … operating systems for handheld computers …”

What is an Operating System?

An operating system (OS) is: a software layer to abstract away and manage details

of hardware resources a set of utilities to simplify application development

Applications

OS

Hardware

Course Aims

Provide an understanding of the technical issues involved in the design of modern distributed (operating) systems

Appreciate the main principles underlying distributed systems: processes, communication, naming, synchronization, replication and consistency, fault tolerance, and security

What is a distributed system?&

What are the design goals?

What is distribution transparency?

Transparency in a Distributed System

Openness in Distributed Systems

An open distributed system Offers services according to standard rules that describe

syntax and semantics of the services Can interact with services from other open systems,

irrespective of the underlying environment

Examples In computer networks, standard rules govern the format,

contents and meaning of messages sent and received In distributed systems, services are specified through

interface description language (IDL)

So, what is Scalability?

How to make a system scale?

Centralized Solutions: Obstacles for Achieving Size Scalability

Examples of scalability limitations.

Concept Example

Centralized services A single server for all users

Centralized data A single on-line telephone book

Centralized algorithms

Doing routing based on complete information

Characteristics of Decentralized Algorithms

No machine has complete information about the system state

Machines make decisions based only on local information

Failure of one machine does not ruin the algorithm

Three is no implicit assumption that a global clock exists

• Internet/World Wide Web

Cloud Computing

A cloud is an elastic execution environment of resources providing a metered service at multiple granularities.

On-demand resource allocation: add and subtract processors, memory, storage.

Amazon Web Services

Elastic Compute Cloud (EC2) Rent computing resources by the hour Basic unit of accounting = instance-hour Additional costs for bandwidth

Simple Storage Service (S3) Persistent storage Charge by the GB/month Additional costs for bandwidth

You’ll be using EC2 for a programming assignment!

What are ACID properties? What do A, C, I, and D represent?

1.4 Internet

intranet

ISP

desktop computer:

backbone

satellite link

server:

network link:

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Instructor’s Guide for Coulouris, Dollimore, Kindberg and Blair, Distributed Systems: Concepts and Design Edn. 5

© Pearson Education 2012

1.4.1 World-Wide-Web

38

1.4.2 Web Servers and Web Browsers

Internet

BrowsersWeb servers

www.google.com

www.uu.se

www.w3c.org

Protocols

Activity.html

http://www.w3c.org/Protocols/Activity.html

http://www.google.comlsearch?q=lyu

http://www.uu.se/

File system ofwww.w3c.org

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Instructor’s Guide for Coulouris, Dollimore, Kindberg and Blair, Distributed Systems: Concepts and Design Edn. 5

© Pearson Education 2012

Announcement

To build our class roster Send our TA Weiyue Xu (weiyue AT cse.unl.edu)

an email with subject “CSCE455/855 roster”, your photo (<2MB) and your name by this Saturday