This document discusses distributed systems and their evolution. It defines a distributed system as a collection of networked computers that communicate and coordinate actions by passing messages. Distributed systems have several advantages over centralized systems, including better utilization of resources and the ability to share information among distributed users. The document describes several models of distributed systems including mini computer models, workstation models, workstation-server models, processor pool models, and hybrid models. It also discusses why distributed computing systems are gaining popularity due to their ability to effectively manage large numbers of distributed resources and handle inherently distributed applications.

1. Prepared by,
V.Santhi,
Assistant Professor,
Department of Computer Applications
Bon Secours College for Women,
Thanjavur

2. Fundamentals
What is Distributed System?
 Single processor, Communication advancement
interconnected multiple processors
 Interconnected multiple processors are basically two
types
1. Tightly Coupled Systems
2. Loosely Coupled Systems

3. Parallel(Tightly coupled) Systems

5. Distributed Computing System
 A distributed system is a collection of processors
interconnected by a communication network in which
each processor has its own local memory and other
peripherals.
 Communication between any two processors of the
system take place by message passing over the
communication network.
 A distributed system is one in which components
located at networked computers communicate and
coordinate their actions only by passing messages

6. 1945-1950 Loading Machine
1950-1960 Batch Processing
1960 Multiprogramming
1960-1970 Time Sharing Systems Mutics, IBM 360
1969-1973 LAN & WAN ARPA Net, Eternet
1960-Early 1980 MiniComputers PDP, VAX
1980s Workstations Altoe
1980-Present Workstation Server
Model
Sprite, V System
1990 Clusters BEOWFUL
Late 1990 Cloud Computing Globus
Evolution of Distributed Computing
System

7. Distributed Computing System
Models
Minicomputer model
 Workstation model
 Workstation-server model
 Processor-pool model
 Cluster model
 Grid computing

8. Mini Computer Model

9.  Extension Centralized Time sharing system
 Few minicomputers interconnected by a communication
network.
 Multiple users
1. User must log on his/her home minicomputer.
2. Thereafter, he/she can log on a remote machine by telnet.
 Resource sharing
1. Database
2. High-performance devices
Ex: ARPAnet

10. Workstation Model(diskful and a
local filesystem)

11.  anSeveral workstations connected by a communication
network
 Workstations equipped with own disk
 At any one time, other workstations idle, resulting in the
waste of CPU time.
 Workstations are interconnect with high speed LAN
 Process migration
 Users first log on his/her personal workstation.
 If there are idle remote workstations, a heavy job may
migrate to one of them

12.  Issues:
 How to find am idle workstation
 How to migrate a job
 What if a user logs onto a workstation which is running a
process of a remote machine (preemptive process migration
facility)


13. Workstation-Server Model(c-s
processes can be on the same m/c
)

14.  Client workstations
Diskless
Graphic/interactive applications processed in local
All file, print, http and even cycle computation
requests are sent to servers.

15.  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)

16.  A Client process calls a server process’
function.
 No process migration invoked so the
response time is guaranteed )
Example: NSF
Advantages
 (cost,maintenance,anywhere,upgradation)

17. Processor-Pool Model

18.  Clients:
They log in one of terminals (diskless workstations or
X terminals)
All services are dispatched to servers.

19.  Servers:
Necessary number of processors are
allocated to each user from the pool.
Better utilization but less interactivity

20.  Pool of backend processors handle processing
–Run server manages the backend processors
–User does not log on to his home m/c ( like in other
models)
 –Better utilization of processing power

21. Hybrid Model
 Combine the advantages of both workstation-server
and the processor-pool model
 Guaranteed response time to interactive jobs
 More expensive to implement

22. Why are Distributed Computing
Systems Graining Popularity
 DOS more complex and difficult to build than
centralized system.
 Increased complexity
 Effectively using &n managing large no of distributed
resources.
 System software of DOS handle communication and
security problems very different than centralized
 Special software needed for loss of messages during
transmission
 Prevent Overloading of the network

23. Inherently Distributed
Applications
 Applications are inherently distributed in nature –
realization
 DOS for collecting, preprocessing and accessing the
data
Ex:
Airline reservation
Banking system

24. Information Sharing among
Distributed Users
 Efficient person – to – person communication facility
by sharing information over great distance
 Information generated by one user efficiently shared
by the users.