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Centralized computing is computing done at a central location, usingterminals that are attached to a central computer. The computer itself may control all theperipherals directly (if they are physically connected to the central computer), or they may be attached via aterminal server. Alternatively, if the terminals have the capability, they may be able to connect to the central computer over the network. The terminals may betext terminals orthin clients, for example.
It offers greatersecurity overdecentralized systems because all of theprocessing is controlled in a central location. In addition, if one terminal breaks down, the user can simply go to another terminal andlog in again, and all of theirfiles will still be accessible. Depending on the system, they may even be able to resume theirsession from the point they were at before, as if nothing had happened.
This type of arrangement does have some disadvantages. The central computer performs the computing functions and controls the remote terminals. This type of system relies totally on the central computer. Should the central computercrash, the entire system will "go down" (i.e. will be unavailable).
Another disadvantage is that central computing relies heavily on the quality of administration and resources provided to its users. Should the central computer be inadequately supported by any means (e.g. size of home directories, problems regarding administration), then your usage will suffer greatly. The reverse situation, however, (i.e., a system supported better than your needs) is one of the key advantages to centralized computing.
The very first computers did not have separate terminals as such; their primitive input/output devices were built in. However, soon it was found to be extremely useful for multiple people to be able to use a computer at the same time, for reasons of cost – early computers were very expensive, both to produce and maintain, and occupied large amounts of floor space. The idea of centralized computing was born. Earlytext terminals used electro-mechanicalteletypewriters, but these were replaced bycathode ray tube displays (as found in 20th century televisions and computers). The text terminal model dominated computing from the 1960s, until the rise to dominance ofhome computers andpersonal computers in the 1980s.
As of 2007, centralized computing is now coming back into fashion – to a certain extent. Cloud computing has had an important role in the return of centralized computing.[1]Thin clients have been used for many years by businesses to reducetotal cost of ownership, whileweb applications are becoming more popular because they can potentially be used on many types of computing device without any need for software installation. Already, however, there are signs that the pendulum is swinging back again, away from pure centralization, asthin client devices become more likediskless workstations due to increased computing power, and web applications start to do more processing on the client side, with technologies such asAJAX andrich clients.
In addition,mainframes are still being used for some mission-critical applications, such as payroll, or for processing day-to-day account transactions in banks. These mainframes will typically be accessed either usingterminal emulators (real terminal devices are not used much any more) or via modern front-ends such asweb applications – or (in the case of automated access)protocols such asweb services protocols.
Some organizations use adiskless node model partway between centralized computing and conventional desktop computing, in which some applications (such asweb browsers) are run locally, while other applications (such as critical business systems) are run on theterminal server. One way to implement this is simply by runningremote desktop software on a standarddesktop computer.
A relatively new method of centralized computing,hosted computing, solves many of the problems associated with traditional distributed computing systems. By centralizing processing and storage on powerful server hardware located in a data center, rather than in a local office, it relieves organizations of the many responsibilities in owning and maintaining an information technology system. These services are typically delivered on a subscription basis by anapplication service provider (ASP).[2]