Centralized computing
Encyclopedia
Centralized computing is computing done at a central location, using terminals
that are attached to a central computer. The computer itself may control all the peripheral
s directly (if they are physically connected to the central computer), or they may be attached via a terminal server
. Alternatively, if the terminals have the capability, they may be able to connect to the central computer over the network. The terminals may be text terminals or thin client
s, for example.
It offers greater security
over decentralized systems
because all of the processing
is controlled in a central location. In addition, if one terminal breaks down, the user can simply go to another terminal and log in again, and all of their file
s will still be accessible. Depending on the system, they may even be able to resume their session
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 computer crash
, 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.
displays (as found in 20th century televisions and computers). The text terminal model dominated computing from the 1960s until the rise to dominance of home computer
s and personal computer
s in the 1980s.
s have been used for many years by businesses to reduce total cost of ownership
, while web application
s 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, as thin client
devices become more like diskless workstation
s due to increased computing power, and web applications start to do more processing on the client side, with technologies such as AJAX
and rich clients.
In addition, mainframe
s 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 using terminal emulator
s (real terminal devices are not used much any more) or via modern front-ends such as web application
s - or (in the case of automated access) protocols
such as web service
s protocols.
s) are run locally, while other applications (such as critical business systems) are run on the terminal server
. One way to implement this is simply by running remote desktop software
on a standard desktop computer
.
(ASP).
Computer terminal
A computer terminal is an electronic or electromechanical hardware device that is used for entering data into, and displaying data from, a computer or a computing system...
that are attached to a central computer. The computer itself may control all the peripheral
Peripheral
A peripheral is a device attached to a host computer, but not part of it, and is more or less dependent on the host. It expands the host's capabilities, but does not form part of the core computer architecture....
s directly (if they are physically connected to the central computer), or they may be attached via a terminal server
Terminal server
A terminal server enables organizations to connect devices with an RS-232, RS-422 or RS-485 serial interface to a local area network . Products marketed as terminal servers can be very simple devices that do not offer any security functionality, such as data encryption and user authentication...
. Alternatively, if the terminals have the capability, they may be able to connect to the central computer over the network. The terminals may be text terminals or thin client
Thin client
A thin client is a computer or a computer program which depends heavily on some other computer to fulfill its traditional computational roles. This stands in contrast to the traditional fat client, a computer designed to take on these roles by itself...
s, for example.
It offers greater security
Security
Security is the degree of protection against danger, damage, loss, and crime. Security as a form of protection are structures and processes that provide or improve security as a condition. The Institute for Security and Open Methodologies in the OSSTMM 3 defines security as "a form of protection...
over decentralized systems
Decentralized computing
Decentralized computing is the allocation of resources, both hardware and software, to each individual workstation, or office location. In contrast, centralized computing exists when the majority of functions are carried out, or obtained from a remote centralized location. Decentralized computing...
because all of the processing
Process (computing)
In computing, a process is an instance of a computer program that is being executed. It contains the program code and its current activity. Depending on the operating system , a process may be made up of multiple threads of execution that execute instructions concurrently.A computer program is a...
is controlled in a central location. In addition, if one terminal breaks down, the user can simply go to another terminal and log in again, and all of their file
Computer file
A computer file is a block of arbitrary information, or resource for storing information, which is available to a computer program and is usually based on some kind of durable storage. A file is durable in the sense that it remains available for programs to use after the current program has finished...
s will still be accessible. Depending on the system, they may even be able to resume their session
Session (computer science)
In computer science, in particular networking, a session is a semi-permanent interactive information interchange, also known as a dialogue, a conversation or a meeting, between two or more communicating devices, or between a computer and user . A session is set up or established at a certain point...
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 computer crash
Crash (computing)
A crash in computing is a condition where a computer or a program, either an application or part of the operating system, ceases to function properly, often exiting after encountering errors. Often the offending program may appear to freeze or hang until a crash reporting service documents...
, 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.
History
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. Early text terminals used electro-mechanical teletypewriters, but these were replaced by cathode ray tubeCathode ray tube
The cathode ray tube is a vacuum tube containing an electron gun and a fluorescent screen used to view images. It has a means to accelerate and deflect the electron beam onto the fluorescent screen to create the images. The image may represent electrical waveforms , pictures , radar targets and...
displays (as found in 20th century televisions and computers). The text terminal model dominated computing from the 1960s until the rise to dominance of home computer
Home computer
Home computers were a class of microcomputers entering the market in 1977, and becoming increasingly common during the 1980s. They were marketed to consumers as affordable and accessible computers that, for the first time, were intended for the use of a single nontechnical user...
s and personal computer
Personal computer
A personal computer is any general-purpose computer whose size, capabilities, and original sales price make it useful for individuals, and which is intended to be operated directly by an end-user with no intervening computer operator...
s in the 1980s.
Contemporary status
As of 2007, centralized computing is now coming back into fashion - to a certain extent. Thin clientThin client
A thin client is a computer or a computer program which depends heavily on some other computer to fulfill its traditional computational roles. This stands in contrast to the traditional fat client, a computer designed to take on these roles by itself...
s have been used for many years by businesses to reduce total cost of ownership
Total cost of ownership
Total cost of ownership is a financial estimate whose purpose is to help consumers and enterprise managers determine direct and indirect costs of a product or system...
, while web application
Web application
A web application is an application that is accessed over a network such as the Internet or an intranet. The term may also mean a computer software application that is coded in a browser-supported language and reliant on a common web browser to render the application executable.Web applications are...
s 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, as thin client
Thin client
A thin client is a computer or a computer program which depends heavily on some other computer to fulfill its traditional computational roles. This stands in contrast to the traditional fat client, a computer designed to take on these roles by itself...
devices become more like diskless workstation
Diskless workstation
A diskless node is a workstation or personal computer without disk drives, which employs network booting to load its operating system from a server...
s due to increased computing power, and web applications start to do more processing on the client side, with technologies such as AJAX
Ajax
- Mythology :* Ajax , son of Telamon, ruler of Salamis and a hero in the Trojan War, also known as "Ajax the Great"* Ajax the Lesser, son of Oileus, ruler of Locris and the leader of the Locrian contingent during the Trojan War.- People :...
and rich clients.
In addition, mainframe
Mainframe computer
Mainframes are powerful computers used primarily by corporate and governmental organizations for critical applications, bulk data processing such as census, industry and consumer statistics, enterprise resource planning, and financial transaction processing.The term originally referred to the...
s 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 using terminal emulator
Terminal emulator
A terminal emulator, terminal application, term, or tty for short, is a program that emulates a video terminal within some other display architecture....
s (real terminal devices are not used much any more) or via modern front-ends such as web application
Web application
A web application is an application that is accessed over a network such as the Internet or an intranet. The term may also mean a computer software application that is coded in a browser-supported language and reliant on a common web browser to render the application executable.Web applications are...
s - or (in the case of automated access) protocols
Communications protocol
A communications protocol is a system of digital message formats and rules for exchanging those messages in or between computing systems and in telecommunications...
such as web service
Web service
A Web service is a method of communication between two electronic devices over the web.The W3C defines a "Web service" as "a software system designed to support interoperable machine-to-machine interaction over a network". It has an interface described in a machine-processable format...
s protocols.
Hybrid client model
Some organisations use a hybrid client model partway between centralized computing and conventional desktop computing, in which some applications (such as web browserWeb browser
A web browser is a software application for retrieving, presenting, and traversing information resources on the World Wide Web. An information resource is identified by a Uniform Resource Identifier and may be a web page, image, video, or other piece of content...
s) are run locally, while other applications (such as critical business systems) are run on the terminal server
Terminal server
A terminal server enables organizations to connect devices with an RS-232, RS-422 or RS-485 serial interface to a local area network . Products marketed as terminal servers can be very simple devices that do not offer any security functionality, such as data encryption and user authentication...
. One way to implement this is simply by running remote desktop software
Remote desktop software
In computing, the term remote desktop refers to a software or an OS feature allowing applications, either command line programs or graphical applications, to be run remotely on a server, while being displayed locally. Remote desktop applications have varying features...
on a standard desktop computer
Desktop computer
A desktop computer is a personal computer in a form intended for regular use at a single location, as opposed to a mobile laptop or portable computer. Early desktop computers are designed to lay flat on the desk, while modern towers stand upright...
.
Hosted computing model
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 an application service providerApplication service provider
An application service provider is a business that provides computer-based services to customers over a network. Software offered using an ASP model is also sometimes called On-demand software or software as a service ....
(ASP).
See also
- UserfulUserfulUserful is a desktop virtualization company that develops software to create Linux-based remotely managed virtual desktops that enable up to 10 users to simultaneously share one computer...
- Time sharing
- Linux Terminal Server ProjectLinux Terminal Server ProjectLinux Terminal Server Project is a free and open source terminal server for Linux that allows many people to simultaneously use the same computer. Applications run on the server with a terminal known as a thin client handling input and output...
- Terminal ServicesTerminal ServicesRemote Desktop Services in Windows Server 2008 R2, formerly known as Terminal Services in Windows Server 2008 and previous versions, is one of the components of Microsoft Windows that allows a user to access applications and data on a remote computer over a network, using the Remote Desktop...
- Multiseat
- Thin clientThin clientA thin client is a computer or a computer program which depends heavily on some other computer to fulfill its traditional computational roles. This stands in contrast to the traditional fat client, a computer designed to take on these roles by itself...
- Computer terminalComputer terminalA computer terminal is an electronic or electromechanical hardware device that is used for entering data into, and displaying data from, a computer or a computing system...