Multiprocessors— Large vs. Small Scale Multiprocessors— Large vs. Small Scale.
INTRODUCTION TO - kcesmjcollege.in OS.pdf · Difference between various computers and the way ......
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Transcript of INTRODUCTION TO - kcesmjcollege.in OS.pdf · Difference between various computers and the way ......
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
