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Distributed Systems Architecture. Presenters Rose Kit & Turgut Tezir. Outline. Introduction to Distributed System Characteristics of Distributed System Advantages of Distributed System Disadvantages of Distributed System Loosely-coupled Systems Tightly-coupled system Array Processor.

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distributed systems architecture

Distributed Systems Architecture

Presenters

Rose Kit & Turgut Tezir

outline
Outline
  • Introduction to Distributed System
  • Characteristics of Distributed System
  • Advantages of Distributed System
  • Disadvantages of Distributed System
  • Loosely-coupled Systems
  • Tightly-coupled system
  • Array Processor
introduction to distributed system
Introduction to Distributed System
  • Centralized System
    • A single computer with one ore more CPUs processes all incoming request
    • Problems with cost, reliability
    • Specification and implementation are defined within a single system
  • Distributed System
    • Opposite of centralized system
    • Set of separate computers that are capable of autonomous operation, link by a compute network.
    • Enable individual computers (different location) to share resources in the network
    • Server implementation for the same interface located in different servers.
characteristics of distributed system
Characteristics of Distributed System
  • Resource sharing
    • Resource provided by a computer which is a member of a distributed system can be shared by clients and other members of the system via a network.
    • “Resource Manager” is a software module (based on set of management policies) that provides interfaces which enables resource to be manipulated by clients, Openness
  • Openness
    • Resource sharing services can be incorporated without disruption or duplication of existing services
  • Concurrency
    • All concurrent access must be synchronised to avoid problems such as lost update, dirty read, incorrect summary & unrepeatable read.
characteristics of distributed system6
Characteristics of Distributed System
  • Scalability
    • flexible to grow in size.
  • Fault tolerance
    • the system appropriately handles errors
    • hardware redundancy, software recovery
  • Transparency
    • hide all unnecessary details from users
    • Example: Location transparency - clients do not need to know the location of the servers
advantages of distributed system
Advantages of Distributed System
  • Shareability
    • Allows systems to use each other’s resources
  • Expandability
    • Permits new systems to be added as members of the overall system
  • Local Autonomy
    • Manage local resources
  • Improved performance
    • Resource replication
    • Combined processing power of multiple computers provides much more processing power than a centralised system with multiple CPUs
  • Improved reliability and availability
    • disruption would not stop the whole system from providing its services as resources spread across multiple computers
  • Potential cost reductions
disadvantages of distributed system
Disadvantages of Distributed System
  • Network reliance
    • problems on network would disrupt activities in the system as a whole
  • Complexities
    • must be able to deal with errors from all computers that make up the distributed system
  • Security
    • private resources would be exposed to a wider range of potential hackers, with unauthorised accesses from any computers connected to the system
    • centralised system is more secure
general types of distributed systems
General Types of Distributed Systems
  • Loosely-Coupled Systems
  • Tightly-Coupled Systems
  • Array Processor Systems
loosely coupled systems
Loosely-coupled Systems
  • Loosely-coupled distributed systems are single-user computers or workstations that are locally networked enabling them to access shared data and resources located in other servercomputers
  • Most distributed systems links two types of computers, workstations and servers (also known as client/server).
  • An early example of the client/server model is the Xerox distributed system
  • Systems with different hardware and software can be networked together
  • Advantages of loosely coupled systems over tightly coupled systems:
    • More scalable.
    • Generally more reliable/fault-tolerant.
    • Allows sharing of widely separated resources.
a loosely coupled system
A Loosely-coupled System

Local Network

Memory

Memory

Memory

Memory

Prg A

Prg B

Prg C

Prg D

Processor

Processor

Processor

Processor

I/O

I/O

I/O

I/O

tightly coupled system
Tightly-coupled system
  • Tightly-coupled system connects a number of processor into an integrated hardware system under the control of a single operating system.
  • The operating system assigns processor and memory space to users’ tasks and allow them to run at the same time.
  • The hardware environment includes a shared memory or a high-speed connection between several separate processor / memory systems with a unified virtual addressing system. This enables users’ tasks to communicate with each other and with the operating system.
  • Advantage of tightly coupled systems over loosely coupled systems:
    • Easier to program but expensive (Limited by the memory bandwidth)
a tightly coupled multiprocessor system
A Tightly-coupled Multiprocessor System

Shared Memory

Program A

Program B

Program C

Program D

Cache Memory

Cache Memory

Cache Memory

Cache Memory

Processor

Processor

Processor

Processor

Input / Output

array processor
Array Processor
  • An array processor is similar to a personal computer with a large number of arithmetic and logic units linked in a regular array. They can be used to perform operations in parallel on arrays of data.
  • The distinguishing characteristics of such a machines is that the entire array of processors obeys a single stream of instructions, some of the instructions being applied to many data items distributed throughout the array of processing unit.
  • There are also other tightly–coupled distributed systems that are designed to make calculations faster by processing them in parallel.
  • Advantages:
    • Useful for achieving high processing speed when processing large regular set of data
  • Disadvantages
    • Geographical distribution
    • Many independent tasks need to executed at the same time.
array processor16
Array Processor

M

M

M

M

M

M

M

M

M

P

P

P

P

P

P

P

P

P

Input / Output

Program

M: Memory

P: Processor