Centralized Systems And Distributed Systems
CENTRALIZED SYSTEMS
The Features Of Centralized Systems:
* Central computer (mainframe) is used ?V usually a large computer (e.g., IBM System 9000) or a minicomputer (e.g., DEC VAX 7000). In terms of company??s structure, a specialized unit is responsible for the management of such computers while its resources are available to all company??s staff. This unit is usually called computer (computing) center.
* Centralized data processing. All data processing operations and calculations are executed by the central computer. The different departments have terminals, linked to the central computer.
* Centralized data. Data is stored in a centralized data storage under the control of the central computer.
* Centralized control. The system administrator is the only one responsible for the data processing system. The system administrator authorizes user access, supports the normal operation and protection of the system.
* Centralized service. Hardware and software are controlled by the computer center staff. Other departments do not have computer specialists.
Example:
Airplane ticket reservation service is a typical example of a centralized system. There is one central computer that serves a lot of ticket sell desks. It keeps up data about all flights and vacancies. All ticked reservation activities are performed in the central computer, while there are terminals only at the sell desks for order input and printing of the results.
Advantages Of Centralized Systems:
The main advantages are:
# easy to manage,
# less personnel costs,
# one computer is enough to support several information systems in the company
DISTRIBUTED SYSTEMS:
The Distributed Systems is the opposite to the centralized system. It comprises computers installed at different sites, each of them performing independent data processing, i.e. accomplishing information services of its own. Usually each computer of the distributed system is specialized to perform a range of activities or support a certain workplace.
Example:
comput ers can be designed for performing project tasks, financial analyses, time scheduling and accounting etc.
The Features Of Distributed Systems:
* Distributed computers. The system is composed of certain number of computers installed at different sites and interconnected by specialized links.
* Distributed data processing. One, several or even all of the computers in the system could be used for problem solving.
* Distributed data. Data, processed by a system, can be distributed among several computers, but it is accessible from any of them.
*
>Distributed control. Distributed systems usually are not under centralized control. The different computers in the system are under the control of the users working with them. Sometimes, distributed control is combined with centralized one. For example, it is usually desirable to look after the special network environment and network status in a centralized way.
Advantages Of Dsitributed Systems:
The main advantages are:
* Quick response. Computer resources in a distributed system are usually distributed so, that the system could process each user request in the fastest possible way.
* Performance. The combined computer operation provides higher performance.
* Reliability. In the case of a centralized systems, if the computer fails, the whole system becomes unusable. No services can be provided until the computer is repaired. If one of the computers in a distributed system fails, its load could be distributed among the other computers. The system continues to function although at lower performance.
* Easy to expand. A distributed system can be expanded much more easily than a centralized one. If a company, using a centralized computer system, decides to raise its productivity, it has to acquire a new computer and try to sell the old one. If the system is a distributed one, its productivity can be raised by acquiring new personal computers or workstations.
* Joint usage of resources. Distributed systems provide this feature. It is quite valuable in cases of using expensive equipment, e.g. laser printers.
* Consistency with company??s structure. It is necessary to relate the structure of the distributed system to the organizational structure of the company. For example, it is natural computers in the accounting department to be assigned accounting tasks, while those in the personnel department - personnel management tasks.
* User participation in system development. A distributed system provides a user with better opportunities to participate in its design and enhancement. Users of distributed systems can not only use its centralized services, but perform independent operations as well.
* Protection (from unauthorized access). Distributed systems are better protected, than centralized ones, because it is possible to appoint people responsible for the protection of each part of the system.
* Flexibility. A distributed system can be more easily tuned to the changing user requirements. Since only some of the users operate with the subsystems, it is possible to modify them with minimum inconvenience.
Computer Technology Achievements Of Distributed Systems:
*
Decrease of computer prices and widespread computers application.The price of the relatively powerful personal computers have decreased to such an extent, that many people could afford them. Besides, these computers provide higher efficiency than large computers of the eighties.
* Development of computer networks.The development of computer communication means made it possible to interconnect computers in local area (LAN), as well as in wide area (WAN) networks. A company computer network can be an example of a local area computer network. Worldwide Internet and SprintNet networks, interconnecting computers, scattered all over the world, are examples of wide area networks
