A client machine that relies on the server to perform the data processing. Either a dedicated thin client terminal or a regular PC with thin client software is used to send keyboard and mouse input to the server and receive screen output in return. The thin client does not process any data; it processes only the user interface (UI). The benefits are improved maintenance and security due to central administration of the hardware and software in the datacenter.
The architecture harks back to the early days of centralized mainframes and minicomputers. In the 1970s and 1980s, a user's machine was a terminal that processed only input and output. All data processing was performed in a centralized server.
There are three ways thin clients are used. The first two are traditional thin clients, processing only the user interface (UI), and the third is a variation that processes the data.
#1 - Shared Services (UI Processing)
Using shared terminal services software such as Windows Terminal Services and Citrix XenApp, users share the operating system and applications in the server with all other users at thin client stations. Although presented with their own desktop, users do not have the same flexibility as they do with their own PC and are limited to running prescribed applications and simple tasks such as creating folders and shortcuts. See Terminal Services and Citrix XenApp.
In the following illustrations, the lines show the conceptual flow of data between the clients and servers. In reality, all clients and servers are wired to a local network switch.
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#2 - Desktop Virtualization (UI Processing)
Using products such as VMware Desktop Manager (VDM) and Citrix XenDesktop, each user's desktop (OS and applications) resides in a separate partition in the server called a "virtual machine." Users are essentially presented with their own PC, except that it physically resides in a remote server in the datacenter. They can modify the desktop and add applications like they could with their own PC (a "fat client"). For details on the virtual machine architecture, see virtual machine. See Citrix XenDesktop and VMware.
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#3 - Browser Based (Data Processing)
This approach uses the same thin client platforms as the first two, but differs in that the user's machine does the data processing. However, it is still a thin client because it is devoid of all applications except for the browser. The applications come from Web servers on the Internet or local LAN, and the data also comes from the servers.
Web-based e-mail is an example of browser-based processing as well as Web-based productivity applications such as Google Apps and Zoho. In some cases, copies of the data can be stored locally, but the software scripts are always downloaded into the user's browser for each session. Years ago, this was the approach of the "network computer," which was developed to compete with Windows PCs (see network computer).
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