A CDE Definition
presentation services protocol
A thin client protocol that provides the format for keyboard and mouse input from the client to the server and screen output from the server to the client. Examples are ICA, RDP and T.share. See thin client.
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, Windows Remote Desktop Services or 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, Remote Desktop 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.
#2 - Desktop Virtualization (UI Processing)
Using products such as VMware Desktop Manager (VDM), the VDI component in Remote Desktop Services and Citrix XenDesktop, each user's desktop (OS and applications) resides in a separate partition in the server called a "virtual machine" (VM). 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 ("fat client"). For details on the virtual machine architecture, see virtual machine. See Remote Desktop Services, Citrix XenDesktop, VMware and desktop virtualization.
#3 - Browser Based (Data Processing)
This approach uses ordinary PCs connected to the Internet, and applications are executed in the Web browser. Although the user's machine does the data processing, it is thin client computing, because the software and data are retrieved from the network. Very little, if anything, is stored locally. If users spend most of their time running Web apps, they are doing thin client computing whether they have a fully loaded PC or not.
Web-based email is the most ubiquitous example of browser-based processing, and Web-based productivity applications such as G Suite and Zoho are also extremely popular (see SaaS). In some cases, copies of the data can be stored locally, but the software scripts that download into the user's browser last for only the current session. Years ago, this was the approach of the "network computer," which failed due to ever diminishing prices of PCs (see network computer). Google's Chromebook is also an example of browser-based thin client computing (see Chromebook).
A True Thin Client
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