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INTRODUCTION TO DISTRIBUTED SYSTEM

NAME: Deepa pawar

ROLL NO.: 311

CLASS:. T.Y.Bsc [IT]

OUTLINE BRIEF HISTORY

WHAT ARE DISTRIBUTED SYSTEM??

ADVANTAGES OF DISTRIBUTED SYSTEM

DISADVANTAGES OF DISTRIBUTED SYSTEM

CHARACTERISTICS OF DISTRIBUTED SYSTEM

GOALS OF DISTRIBUTED SYSTEM

- Resource sharing

- Openness

- Scalability

- Transparency

HARDWARE CONCEPT

SOFTWARE CONCEPT

HISTORY 1945 – 1985

- Computers were large and expensive

- No way to connect them

- All system were centralized systems.

Mid – 1980s

- Powerful microprocessors

- High speed Computer Networks(LANs , WANs).

Then come the

DISTRIBUTED SYSTEMS……….

WHAT ARE DISTRIBUTED SYSTEMS??

A Distributed system is a piece of software that ensures that:

• a collection of independent computers appears to its users as a single computer

Two aspects:

(1) Independent computers and

(2) Single system

Example:

World Wide Web(www)

Others are

The internet

The intranet which is a portion of the internet managed by an organization .

ADVANTAGES Data sharing:

allow many users to access to common database.

Resource sharing Expensive peripherals like color printers.

Communication Enhance human-to-human communication. E.g.: email, chat

Reliability If one machines crashes, the system as a whole can still

survive.

DISADVANTAGES OF DISTRIBUTED SYSTEM

Networking:

The network may lose message and/or become overloaded. Rewiring the network can be costly and difficult.

Software:

Designing, implementing and using distributed software may be difficult. Little software exist at present for distributed system.

Security:

Security becomes a far greater concern. Easy and convenient data access from anywhere creates security problems.

Characteristics of distributed system Difference between various computers and the way

in which they communicate are hidden from user.

Users and application can interact with a distributed system in a consistent ,uniform way, regardless of where and when interaction take place.

Distributed system should also be relatively easy to expand or sale.

A distributed system will normally be continouslyavailable.

GOALS OF DISTRIBUTED SYSTEM Resource sharing :

• With Distributed systems, it is easier for users to access remote resources with other users.

Examples: Printers, files, web pages, etc.

Openness:• The openness of DS is determined primarily by the degree to

which new resource-sharing services can be added and be made available for use by a variety of client program.

Scalability: A system is described as scalable if it remains effective where

there is a significant increase in the number of resources and the number of users.

Transparency:

It hides the fact that the processes and resources are physically distributed across multiple computers.

Transparency is of various forms as follow:

Transparency Description

Location Hide where a resource is located.

Access Hide differences in data representation and how a resource is accessed.

Migration Hide that a resource may move to another location.

Concurrency Hide that a resource may be shared by several competitive users.

Failure Hide the failure and recovery of a resource.

Replication Hide that a resource is replicated

Hardware Concepts

1.6

Different basic organizations and memories in distributed computer

systems

Multiprocessors System:• In multiprocessors system all the CPUs have direct access to the shared memory.

A bus-based multiprocessor: This consist of some number of CPUs, all connected to a common bus along with memory .

To build more than 256 processor, different method is needed to connect CPUs with memory using-

a) A crossbar switch

b) An omega switching network

1.8

Homogeneous Multicomputer Systems

a) Grid/Mesh: Grids are easy to understand and have 2-dimentional nature.

b) Hypercube: It is an n-dimentional cube.

1-9

Software Concepts

An overview of

• DOS (Distributed Operating Systems)

• NOS (Network Operating Systems)

• Middleware

System Description Main Goal

DOSTightly-coupled OS for multi-processors and homogeneous multicomputers

Hide and manage hardware resources

NOSLoosely-coupled OS for heterogeneous multicomputers (LAN and WAN)

Offer local services to remote clients

MiddlewareAdditional layer atop of NOS implementing general-purpose services

Provide distribution transparency