Article:
  Distributed Systems Topologies: Part 2
Subject:   Centralized and Decentralized systems
Date:   2003-01-01 10:22:43
From:   anonymous2
Hello Nelson Minar,


I have red your great article dated on 14/12/2001 and its title is
“ Distributed Systems Topologies: Part 1”
I found myself confused to distinguish between the
The term “CENTRALIZED SYSTEM”
And the term “DISTRIBUTED SYSTEM”
Please can you answer me the following questions
To become clear to me the distinction B/W these two systems:
1. does “Decentralized system” same as the “Distributed system”
in concept? And just the difference in terms only?
2. what is the major difference B/W “Centralized system” and “Distributed system”?
is the difference that: in Centralized system all the Applications interfaces, computational process(functionalities), and data retrieval are in the central machine(such as Mainframe) where as the clients are dummies and do not contribute in any functionality except as I/O devices(i.e. clients are just keyboards and monitors. And do not have processors and storage devices in themselves).
And in Distributed system not all the functionality are in the central machine(server). instead, the clients share the server in some computational process and functionality(therefore they are not dummies in the sense that they have processors and storage devices, …etc).
3. you mentioned that : “The debate between centralized and decentralized systems is fundamentally about topology -- in other words, how the nodes in the system are connected. Topology can be considered at many different levels: physical, logical, connection, or organizational.”
Can you make it clear to me the difference between:
“Physical and Connecting” and between
“Logical and Organizational” in the context.
4. You mentioned: “Centralized+Centralized” and
“Centralized+DeCentralized” as two of the Basic Distributed systems topologies.
Did you mean that, in the “Centralized+Centralized” there is NO connection between the clients themselves(here, in this case the stacked servers which are central nodes for other nodes), but the connection is between each of them to the central server directly. where as in the “Centralized+DeCentralized” there is a connection between them and this connection is also connected to the central machice(server)?


Thank you for your time and efforts.
With lot of respect


Hikmat Jaber
hikmat101@hotmail.com
hikmat99@maktoob.com


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  • Nelson Minar photo Centralized and Decentralized systems
    2003-02-17 10:05:37  Nelson Minar | O'Reilly Author [View]

    The term "distributed system" means different things to different people. I use it to mean any system that involves a network. In that usage centralized, decentralized, rings, hybrids, etc are all "distributed systems".

    [logical vs physical topology]
    My article is a bit sloppy on this point. One way you can look at a topology is the physical fact of how the bits move from machine to machine, the details of the routing. That view can be nonsensical; for instance all Internet systems are in some sense decentralized because that's the way Internet routing works. So it's often useful to look more at the logical structure of the system. oreilly.com is logically a single centralized web site, even if physically the site itself is organized as a ring and your web browser's packets get there via a decentralized system.

    [centralized+decentralized connections]
    In the centralized+decentralized system I describe in the article, what I mean is that you have a group of decentralized hosts acting as centralized servers to leaf clients. I recommend taking a look at the KaZaA/FastTrack design and its use of supernodes as a good example of this.