2.4 Thin Clients (Terminals ?)
Introduction
Since "thin clients" are not text terminals, this HOWTO only provides a brief overview of them. There are other HOWTOs that cover them in more detail. See Related HOWTOs, etc.. Thin clients are thin (minimal) client computers that behave something like terminals. Since text terminals (except for very old ones) run an embedded operating system, they are also like a computer. Thin-clients need more computing power. In contrast to text-terminals thin clients all display a modern high-speed GUI. They are dependent on more powerful computers (servers) for their operation. For a true thin client terminal, the computing work and disk storage will all be done on the server. At the other extreme, most of this work and storage is done at the thin client but some things such as administration, still depend on the server. Since such a client is not really "thin" it may more correctly be called a "fat client".
Such clients may be created from an ordinary PC by using software or may be a stand-alone piece of hardware. But the stand-alone hardware will often use a conventional PC monitor plus a small box for the computer part of the hardware. Linux seems to favor the use of PCs as a client.
Some claim that text-terminals are also thin clients but they are not really since they don't conform to the client-server model. However, connecting a terminal via telnet does invoke the client-server model in the use of telnet as a means of transport of data. But the relation of the text-terminal to it's host is not one of client-server. The text-terminal is just another means of access to the computer just like the monitor and its keyboard is. One could apply this same reasoning to a thin client and say that the client-server relationship is only for the transport of data.
Thus a thin client is like a terminal. It has a GUI with a mouse that makes it seem like you are using a computer. You are, but that computer may be far away and have many other people using it at the same time you are. Communication is over a high speed network cable or even over the Internet. Some thin clients can, in addition, emulate a text terminal and have a serial port connector for that purpose. One even has a USB interface.
There are various types of thin clients. One type is the "Window Terminal" which runs under MS servers (and software). Another type is the "network computer" which is supposed to be platform neutral. This implies they should work with both MS Windows and Linux but early models may not be easy to use with Linux. For Linux, the X Window protocol is used. See Thin clients and NCs under Linux
MS Window terminals
These are true terminals since all the computing work is done by a server running Windows. They are also called "Window-based Terminals" (WBT). These terminals (clients) are something like computers since they often run an embedded operating system such as Linux or Microsoft's CE, NT, or XP. It's often stored in flash memory so that it may be updated. Also, ordinary PCs can be used as clients (including, in some cases, Linux PCs) with the appropriate software, Some clients can support X Window (from a Linux server) and some can emulate text-terminals. Many so called "network computers" can also run X Window. This will be discussed in the next section.
The server for these clients usually runs MS's Terminal Services (for Windows 2000 servers). Prior to this there was Windows NT Terminal Server Edition (starting mid 1998 with codename "Hydra"). MS uses RDP (Remote Desktop Protocol) which is based on the ITU T.120 protocol. In addition, there is an optional ICA protocol (with added features) which can inter-operate with RDP.
Prior to this there was a modified Windows NT 3.51 (1995) called "WinFrame" by Citrix using the proprietary ICA protocol (Independent Computing Architecture). After MS came out with its own terminal server, Citrix still remained on the scene. It created MetaFrame software (formerly pICAsso) as an add-on to MS's
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