Distributed Systems Unit – 1 Concepts of DS By :- Maulik V. Dhamecha Maulik V. Dhamecha (M.Tech.)

Centralized vs. Distributed Computing Early computing was performed on a single processor and this Uni-processor computing can be called centralized computing. A distributed system is a collection of independent computers, interconnected via a network, capable of collaborating on a task. Eg. Internet, intranet, ATM Maulik V. Dhamecha (M.Tech.)

Distributed computing Models Workstation model Workstation-server model Processor-pool model Maulik V. Dhamecha (M.Tech.)

Workstation Model This work station mode consists of a network of personal computers. Its known as diskful workstation. Problems: How to find an idle workstation How to migrate a job What if a user log on the remote machine 100Mbps LAN Workstation Maulik V. Dhamecha (M.Tech.)

Workstation-Server Model Client workstations – Diskless – Graphic/interactive applications processed in local – All file, print, http and even cycle computation requests are sent to servers. Server minicomputers – Each minicomputer is dedicated to one or more different types of services. Client-Server model of communication – RPC (Remote Procedure Call) – RMI (Remote Method Invocation) A Client process calls a server process ’ function. No process migration invoked Example: NFS 100Gbps LAN Workstation Mini- Computer file server Mini- Computer http server Mini- Computer cycle server Maulik V. Dhamecha (M.Tech.)

Processor-Pool Model Clients: – They log in one of terminals (diskless workstations or X terminals) – All services are dispatched to servers. Servers: – Necessary number of processors are allocated to each user from the pool. Server 1 100Mbps LAN Server N Maulik V. Dhamecha (M.Tech.)

Software concepts Network operating system Distributed operating system Multiprocessor time-sharing system Maulik V. Dhamecha (M.Tech.)

Design Issues of Distributed Systems Network Transparency Flexibility Reliability Performance Scalability Security Fault Tolerance Maulik V. Dhamecha (M.Tech.)

1. Network 2. Transparency How to achieve the single-system image, i.e., how to make a collection of computers appear as a single computer. Maulik V. Dhamecha (M.Tech.)

Types of transparency Location Transparency: users cannot tell where hardware and software resources such as CPUs, printers, files, data bases are located. Migration Transparency: resources must be free to move from one location to another without their names changed. Replication Transparency: OS can make additional copies of files and resources without users noticing. Concurrency Transparency: The users are not aware of the existence of other users. Maulik V. Dhamecha (M.Tech.)

3. Flexibility Make it easier to change 4. Reliability Distributed system should be more reliable than single system. 5. Performance 6. Scalability Systems grow with time Maulik V. Dhamecha (M.Tech.)

7. Security 8. Fault Tolerance Maulik V. Dhamecha (M.Tech.)

Client-Server Model Use TCP/IP for reliable network connection. This implies the client must establish a connection before sending the first request. Maulik V. Dhamecha (M.Tech.)

World Wide Web www 1.0 www 2.0 Maulik V. Dhamecha (M.Tech.)