Unit-1:Distributed Operating System - Darshan Institute of Engineering ...

1 .Dipak Ramoliya  dipak.ramoliya@darshan.ac.in Computer Engineering Darshan Institute of Engineering & Technology Unit: 1 Introductory Concepts of Distributed Operating System Distributed Operating System (2160710)

2 .Distributed Operating System – Teaching Schemes

3 .Distributed Operating System – Teaching Schemes

4 .Distributed Operating System – Teaching Schemes

5 .Distributed Operating System - Book

6 .Unit Outline & Weightage % 1. Introduction to Distributed System 15% Operating System Basic Concepts of Distributed Operating System Definition and Goal Advantage Hardware and Software Concepts Design Issues

7 .What is Operating System? An operating system (OS) is system software that manages computer hardware and software resources and provides common services for computer programs . Example:

8 .What is Operating System? It is a program that acts as an interface between the user and the computer hardware and controls the execution of all kinds of programs .

9 .What is Distributed Operating System? Definition by Coulouris , Dollimore , Kindberg and Blair A distributed system is defined as one in which components at networked computers communicate and coordinate their actions only by passing messages. This definition allows for concurrent execution of programs, but prevents the possibility of a global clock and means that components can fail independently of one another .

10 .What is Distributed Operating System? Definition by Andrew S. Tannenbaum and Maarten Van Steen A Distributed System is a collection of independent computers that appears to its users as a single coherent system . ... or ... as a single system.

11 .Example of Distributed Systems From the definition, Distributed Systems also looks the same as single system . Let us say about Google Web Server , from users perspective while they submit the searched query, they assume google web server as a single system. Just visit  google.com , then search. However , under the hood Google builds a lot of servers even distributes in different geographical area to give you a search result within few seconds. So the Distributed Systems does not make any sense for normal users. But CEO, CIO or management level should really take care of it for better giving the organizational image by providing the best and on time service to customers .

12 .Examples of Distributed Systems A typical portion of the Internet global access to “everybody ”( data, service, other actor) enormous size ( open ended ) No single authority intranet ISP desktop computer: backbone satellite link server: % network link: % % %

13 .Examples of Distributed Systems A typical intranet a single authority protected access - a firewall - total isolation typical services: - infrastructure services: file service, name service - application services

14 .Examples of Distributed Systems Web Search Engines: Major growth industry in the last decade. 10 billion per month for global number of searches. e.g . Google distributed infrastructure Massively multiplayer online games: Large number of people interact through the Internet with a virtual world. Challenges include fast response time, real-time propagation of events.

15 .Why Distributed Operating System? The main answer is to cope with the extremely higher demand of users in both processing power and data storage. For example, according to  www.datacenterknowledge.com : Facebook by the end of 2010 Total users: 500 millions Total servers: 60, 000 servers (estimate, Oct 2009) 50 millions operations per second 1 million photos are viewed every second Each month more than 3 billions photos are uploaded With this extremely demand, I do believe single system could not achieve it. That’s one reason why distributed systems comes in place. There are many reasons that make distributed systems is viable such as high availability, scalability, resistant to failure, etc.

16 .Why Distributed Operating System? The main answer is to cope with the extremely higher demand of users in both processing power and data storage. For example, according to  www.datacenterknowledge.com : Facebook by the end of 2010 Total users: 500 millions Total servers: 60, 000 servers (estimate, Oct 2009) 50 millions operations per second 1 million photos are viewed every second Each month more than 3 billions photos are uploaded With this extremely demand, I do believe single system could not achieve it. That’s one reason why distributed systems comes in place. There are many reasons that make distributed systems is viable such as high availability, scalability, resistant to failure, etc.

17 .A distributed system organized as Middleware . The middleware layer runs on all machines, and offers a uniform interface to the system. Distributed Operating System Architecture

18 .Middleware (MW) Software that manages and supports the different components of a distributed system. In essence, it sits in the middle of the system. Middleware is usually off-the-shelf rather than specially written software. Examples: Transaction processing monitors Data converters Communication controllers

19 .Role of Middleware (MW) In some early systems : MW tried to provide the illusion that a collection of separate machines was a single computer. E.g. NOW project: GLUNIX middleware (Global Layer Unix) Today: Clustering software allows independent computers to work together closely MW also supports seamless access to remote services, doesn’t try to look like a general-purpose OS. Other Middleware Examples CORBA (Common Object Request Broker Architecture) DCOM (Distributed Component Object Management) – being replaced by .NET Sun’s ONC RPC (Remote Procedure Call) RMI (Remote Method Invocation) SOAP (Simple Object Access Protocol)

20 .Distributed System Goals The following are the main goals of distributed systems: The relative simplicity of the software - each processor has a dedicated function. Incremental growth - if we need 10 percent more computing power, we just add 10 percent more processors. Reliability and availability - a few parts of the system can be down without disturbing people using the other parts . Openness: Offer services according to standard rules that describe the syntax and semantics of those services.

21 .Advantages of Distributed Systems over Centralized Systems Economics: A collection of microprocessors offer a better price/performance than mainframes. Low price/performance ratio: cost effective way to increase computing power. Speed: A distributed system may have more total computing power than a mainframe. Inherent distribution: Some applications are inherently distributed. Ex . a supermarket chain. Reliability: If one machine crashes, the system as a whole can still survive. Higher availability and improved reliability.

22 .Advantages of Distributed Systems over Independent PCs Data sharing: allow many users to access to a common data base Resource Sharing: expensive peripherals like color printers Communication: enhance human-to-human communication, e.g., email, chat Flexibility: spread the workload over the available machines

23 .Classification of Distributed System

24 .Classification based on Hardware Tightly Coupled Loosely Coupled Sequent, Encore Ultra Computer, RP3 Workstation on LAN Hypercube, Transputer Even though all distributed system consist of multiple CPUs, there are several different ways the hardware can be organized, specially in terms of how they are interconnected and communicate.

25 .Classification based on Hardware Loosely-coupled OS A collection of computers each running their own OS, OS’s allow sharing of resources across machines Manages heterogeneous multicomputer Distributed Systems. Difference: provides local services to remote clients via remote logging Data transfer from remote OS to local OS via FTP (File Transfer Protocols) Network Operating System (NOS) Tightly-coupled OS OS tries to maintain single global view of resources it manages. Manages multiprocessors & homogeneous multicomputer . Similar “local access feel” as a non-distributed, standalone OS. Data migration or computation migration modes (entire process or threads) Distributed Operating System (DOS)

26 .Classification based on Instruction & DataStream According to Flynn, classification can be done based on the number of instruction streams and number of data streams. Single instruction stream single data stream ( SISD) All traditional uniprocessor computers (those having 1 CPU) fall in this category, from personal computers to large mainframes. Single instruction stream, multiple data streams (SIMD) This type refers to array processors with one instruction unit that fetches an instruction and then commands many data units to carry it out in parallel, each with in its own data.

27 .Classification based on Instruction & DataStream Multiple instruction streams, single data stream (MISD ) No more computers fit this model. Uncommon architecture which is generally used for fault tolerance. Multiple instruction streams, multiple data streams (MIMD ) A group of independent computers, each with its own program counter, program, and data . All distributed systems are MIMD, We divide all MIMD computers into two groups: Have shared memory, usually called multiprocessors . Do not have shared memory, called multicomputer.

28 .Distributed Computing System Models Distributed Computing system models can be broadly classified into five categories.

29 .Minicomputer Model It consists of a few minicomputers interconnected by a communication network. Each minicomputer usually has multiple users logged on to it simultaneously. For this several interactive terminals are connected to each mini computer. Each user is logged onto one minicomputer, with remote access to other minicomputers. The network allows the user to access remote resources that are available on some machine other than the user is currently logged. Minicomputer model can be used for resource sharing like information databases. ARPAnet is the example Distributed computing system based on the minicomputer model.