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Distributed Systems Architecture

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Title: Distributed Systems Architecture


1
Distributed Systems Architecture
  • Presenters
  • Rose Kit Turgut Tezir

2
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

3
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.

4
Distributed and Centralized Computer System
5
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.

6
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

7
Advantages of Distributed System
  • Shareability
  • Allows systems to use each others 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

8
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

9
General Types of Distributed Systems
  • Loosely-Coupled Systems
  • Tightly-Coupled Systems
  • Array Processor Systems

10
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 server
    computers
  • 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.

11
Loosely-coupled Systems
12
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
13
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)

14
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
15
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 tightlycoupled 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.

16
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
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