Comparative Study of DOS and NOS

DISTRIBUTED SYSTEM

A distributed system is a collection of independent computers that appears to its users as a single coherent system

Important characteristics of distributed systems

- Differences between the various computers and the ways in which they communicate are hidden from users

- Users and applications can interact with a distributed system in a consistent and uniform

way, regardless of where and when interaction takes place

Goals of Distributed System

4 important goals that should be met to make building a distributed system worth the effort they are

1) Easily connect Users to resources, hide the fact that resources are distributedacross a network, open, scalable

Forms of Transparency in a Distributed System

Transparency Description

AccessHide differences in data representation and how a resource is accessed

Location Hide where a resource is located

Migration Hide that a resource may move to another location

RelocationHide that a resource may be moved to another location while in use

ReplicationHide that a resource may be shared by several competitive users

ConcurrencyHide that a resource may be shared by several competitive users

Failure Hide the failure and recovery of a resource

PersistenceHide whether a (software) resource is in memory or on disk

2) Transparency

A distributed system that is able to present itself to users and applications as if it were only a single computer system is said to be transparent. Which hides whether a Implementation i.e. software resource is in main memory or disk

3) Openness

An open distributed system is a system that offers services according to standard rules.

4) Scalability

Scalability of a system can be measured along at Least three different dimensions

-First, a system can be scalable with respect to its size, we can easily add more users and resources to the system.

-Second, a geographically scalable system users and resources may lie far apart.

-Third, a system can be administratively scalable; it can still be easy to manage even if it spans many independent administrative organizations.

Hardware Concepts• General Classification:

– Multiprocessor – a single address space among the processors

– Multicomputer – each machine has its own private memory.

• OS can be developed for either type of environment.

• Bus Based or Switch Based Architecture Of memory and processor.

Hardware Concepts

1.6

Basic organizations and memories in distributed computer systems

Multiprocessors

A bus-based multiprocessor.

1.7

Multiprocessors

A crossbar switch An omega switching network

Software Concepts• DOS (Distributed Operating Systems)• NOS (Network Operating Systems)• Middleware

System Description Main Goal

DOSTightly-coupled operating system for multi-processors and homogeneous multicomputers

Hide and manage hardware resources

NOSLoosely-coupled operating system for heterogeneous multicomputers (LAN and WAN)

Offer local services to remote clients

MiddlewareAdditional layer a top of NOS implementing general-purpose services

Provide distribution transparency

Uniprocessor Operating Systems

• Separating applications from operating system code through a microkernel– Can extend to multiple computers

Network Operating System

• OS uses can be different (Windows or Linux)• Typical services: rlogin, rcp

– Fairly primitive way to share files

NOS

• A network operating system (NOS) is a computer operating system that is designed primarily to support workstation, personal computer, and, in some instances, older terminal that are connected on a local area network (LAN). Artisoft's LANtastic, Banyan VINES, Novell's NetWare, and Microsoft's LAN Manager are examples of network operating systems.

• A network operating system provides printer sharing, common file system and database sharing, application sharing, and the ability to manage a network name directory, security, and other housekeeping aspects of a network.

• Example of Network Operating system :

1)Windows NT (2000,XP)2) Ubuntu3)Linux

Network Operating System

• Can have one computer provide files transparently for others (NFS)

Systems, network operating systems do not assume that the underlying hardware is homogeneous

Distributed Operating Systems

• But no longer have shared memory– Provide message passing– Can try to provide distributed shared memory

• But tough to get acceptable performance

DOS

• An OPERATING SYSTEM which manages a number of computers and hardware devices which make up a DISTRIBUTED SYSTEM. Such an operating system has a number of functions: it manages the communication between entities on the system

• Example of Distributed Operating System : -•  • Online Reservation Systems • Online banking

NOS DOS

1) Most current operating systems are capable of using the TCP/IP networking protocols. This means that one system can appear on a network of the other and share resources such as files, printers, and scanners using either wired or wireless connections.

1Distributed computing is a method of computer processing in which different parts of a program run simultaneously on two or more computers that are communicating with each other over a network. Distributed computing is a type of segmented or parallel computing.)

2) A network operating system (NOS) is a piece of software that controls a network and its message (e.g. packet) traffic and queues, controls access by multiple users to network resources such as files, and provides for certain administrative functions, including security.

2) Distributed computing is a type of segmented or parallel computing. But the latter term is most commonly used to refer to processing in which different parts of a program run simultaneously on two or more processors that are part of the same computer.

3) Network OS follows 2 tier Client server architecture 3) Distributed OS follows n tier client/server architecture

4) A network operating system is most frequently used with local area networks and wide area networks, but could also have application to larger network systems.The upper 5 layers of the OSI Reference Model provide the foundation upon which many network operating systems are based.

4) i)Tightly coupled (clustered) — refers typically to a set of highly integrated machines that run the same process in parallel, subdividing the task in parts that are made individually by each one, and then put back together to make the final result.ii)Peer-to-peer — an architecture where there is no special machine or machines that provide a service or manage the network resources. Instead all responsibilities are uniformly divided among all machines, known as peers. Peers can serve both as clients and servers.

5) A Network OS is not the same as the networking tools provided by some existing OSs, Windows XP for instance. An NOS is an OS that has been specifically written to keep networks running at optimal performance.

5) Distributed computing implements a kind of concurrency. It interrelates tightly with concurrent programming so much that they are sometimes not taught as distinct subjects==>Multiprocessor systems,Multicore systems,Computer clusters,Multicomputer systems,Grid computing

Why Middleware ?

Distributed operating system is not intended to handle a collection of independent computers, while network operating system does not provide a view of a single coherent system

So an additional layer of software that is used in network operating systems to more or less hide the heterogeneity of the collection of underlying platforms but also to improve distribution transparency

Distributed System as Middleware

Middleware Models And Present Technologies

1 )Remote Procedure Calls (RPCs).

2 )CORBA

3 )Remote Method Invocation (RMI).

4 )Enterprise Java Beans (EJB).

5 )Component Object Modeling & Distributed Component Object Modeling (COM AND DCOM with .net )

6 )Web Services And SOA (Service Oriented Architecture)

References

1)Distributed Systems by Andrew Tanenbaum

2) Distributed Computing by Sunita Mahajan and Seema shah,Oxford Press

3 )Middleware and Enterprise Integration Technologies by G. SUDHA SADASIVAM, RADHA  SHANKARMANI

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