What is meant by Distributed Operating System

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.