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239 lines
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<TITLE> Text-Terminal-HOWTO: Thin Clients Terminals </TITLE>
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<H2><A NAME="s3">3.</A> <A HREF="Text-Terminal-HOWTO.html#toc3">Thin Clients Terminals </A></H2>
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<H2><A NAME="ss3.1">3.1</A> <A HREF="Text-Terminal-HOWTO.html#toc3.1">Introduction </A>
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</H2>
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<P> Since "thin clients" are not text terminals, this HOWTO only
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provides a brief overview of them. There are other HOWTOs that cover
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them in more detail but (as of 2010) they are unfortunately not up to
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date. See
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<A HREF="Text-Terminal-HOWTO-1.html#related_howtos">Related HOWTOs, etc.</A>. Thin
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clients are thin (minimal) client computers that behave something like
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terminals. Since text terminals (except for very old ones) run an
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embedded operating system, they are also like a computer. In contrast
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to text-terminals, thin clients all display a modern high-speed GUI.
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They are dependent on more powerful computers (servers) for their
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operation. </P>
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<P>For a true thin client terminal, the computing work and
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disk storage will all be done on the server. At the other extreme,
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most of this work and storage is done at the thin client but some
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things such as administration, still depend on the server. Since such
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a client is not really "thin" it may more correctly be called a "fat
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client".</P>
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<P>Instead of "thin client" they could have been simply called "graphic
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terminals" but promoters of this technology wanted a catchy name to
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get customers to believe that it was perhaps a totally different
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technology. This trend of renaming what is basically just graphic
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terminals (with new features) continues unabated. Some of these names
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are "Virtual Desktop" and "Cloud Computing".</P>
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<P>Thin clients may be created from an ordinary PC by using software or
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may be a stand-alone piece of hardware. But such stand-alone hardware
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may often be just a conventional PC monitor plus a small box for the
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computer part of the hardware. Linux seems to favor the use of PCs as
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clients.</P>
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<P>Some claim that text-terminals are also a type of thin client but they
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are not really since they don't conform to the client-server model.
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However, connecting a terminal via telnet does invoke the
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client-server model in the use of telnet as a means of transport of
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data. But the relation of the text-terminal to it's host is not one
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of client-server. The text-terminal is just another means of access
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to the computer just like the monitor and its keyboard is to access a
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PC. One could apply this same reasoning to a thin client and say that
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the client-server relationship is only for the transport of data.</P>
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<P>Thus a thin client is like a terminal. It has a GUI with a mouse that
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makes it seem like you are using a computer. You are, but that
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computer may be far away and have many other people using it at the
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same time you are. Communication is over a high speed network
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(wireless and/or cable) or even over the Internet. Some thin clients
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can, in addition, emulate a text terminal and have a serial port
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connector for that purpose. Recent ones also have USB interfaces as
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well as ethernet.</P>
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<P>There are various types of thin clients. One type is the "Window
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Terminal" which runs under MS servers (and software). Another type is
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the "network computer" which is supposed to be platform neutral. This
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implies they should work with both MS Windows and Linux but early
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models may not be easy to use with Linux. For Linux, the X Window
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protocol is used. See
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<A HREF="#linux_thin_clients">Thin clients and NCs under Linux</A></P>
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<H2><A NAME="ss3.2">3.2</A> <A HREF="Text-Terminal-HOWTO.html#toc3.2">MS Window terminals</A>
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</H2>
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<P>These are true terminals since all the computing work is done by a
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server running Windows. They are also called "Window-based Terminals"
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(WBT). These terminals (clients) are something like computers since
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they often run an embedded operating system such as Linux or
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Microsoft's CE, NT, or XP. It's often stored in flash memory so that
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it may be updated. Also, ordinary PCs can be used as clients
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(including, in some cases, Linux PCs) with the appropriate software,
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Some clients can support X Window (from a Linux server) and some can
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emulate text-terminals. Many so called "network computers" can also
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run X Window. This will be discussed in the next section.</P>
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<P>The server for these clients usually runs MS's Terminal Services (for
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Windows 2000 servers). Prior to this there was Windows NT Terminal
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Server Edition (starting mid 1998 with codename "Hydra"). MS uses RDP
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(Remote Desktop Protocol) which is based on the ITU T.120 protocol.
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In addition, there is an optional ICA protocol (with added features)
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which can inter-operate with RDP.</P>
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<P>Prior to this there was a modified Windows NT 3.51 (1995) called
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"WinFrame" by Citrix using the proprietary ICA protocol (Independent
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Computing Architecture). After MS came out with its own terminal
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server, Citrix still remained on the scene. It created MetaFrame
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software (formerly pICAsso) as an add-on to MS's Terminal Server (or
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Services) so that it could support ICA-based terminals and provide
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other additional features. Before MS got into the act, there were
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other proprietary systems for terminals that could display the MS
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Windows GUI but later on they all switched to support Microsoft's
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system.</P>
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<P>PCs running Linux can be turned into ICA based client terminals using
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"free" (in price only) proprietary ICA client software from Citrix:
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<A HREF="http://support.citrix.com/article/CTX879408">Installing the Linux Client</A>. Unfortunately, MS requires that you purchase a
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license to cover the clients, even if the clients all run Linux. So
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if you want to save money on software costs by using Linux, you'll
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have to go all-Linux and use both Linux servers and clients using the
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free X-Window protocol.</P>
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<P>The above is sometimes called "network computing" since the terminals
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and servers connect to each other over a network (such as the common
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TCP/IP based network used by both Linux and MS). Network computers
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may be somewhat different as described below.</P>
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<H2><A NAME="ss3.3">3.3</A> <A HREF="Text-Terminal-HOWTO.html#toc3.3">Network computers (NC's) </A>
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</H2>
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<P>See
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<A HREF="http://en.wikipedia.org/wiki/Network_Computer">Network Computer - Wikipedia</A> which claims that NC's are
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defunct as a type of hardware, but that NC is used as a synonym for
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"thin client".</P>
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<P>These are neither true computers nor true terminals but are
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something in-between. One type of network computer (NC's) is a
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computer with a CPU but no hard Disk. The OS it needs to run is sent
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to it over a network. NCs are full-graphics and use the services of a
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server computer. They are a little different from terminals since
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some (or most) of the programs they run may execute on their own CPU
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chip. Running a browser was supposed to be one of their primary
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functions and thus Java code applets may be sent to them for
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execution. Many NCs support X Window so that one may use a Linux
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server to support it. Such a server may be called a "Linux Terminal
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Server". IBM called their NC a "NetStation" but now calls it
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"NetVista". They should work on Intranet type networks and NetVista
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can run the Linux OS.</P>
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<P>Wintel came out with a "NetPC" which, unlike the above, is almost a PC
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computer. However, it has no removable disks so users can't install
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their own software or obtain copies of anything.</P>
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<H2><A NAME="linux_thin_clients"></A> <A NAME="ss3.4">3.4</A> <A HREF="Text-Terminal-HOWTO.html#toc3.4">Thin clients and NCs under Linux </A>
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</H2>
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<P> There is a "Linux Terminal Server Project" (LTSP or ltsp) to use
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Linux as a server for diskless thin clients. They use X Window and by
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default, applications run on the server. But with additional effort,
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one can set it up so that some or all applications run on the
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"terminal". See
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<A HREF="http://www.ltsp.org/">http://www.ltsp.org/</A>. </P>
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<P>"Terminal" in LTSP is actually a thin (or fat) client. This project's
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client can also run a telnet session and thus behave like a
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text-terminal. A software package named "lts" for the LTSP is
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available in the major Linux distributions.</P>
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<P>It's claimed that if one has only a few "terminals", they will work
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without the ltsp software. But if one has many "terminals", ltsp
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software is needed. So use ltsp if what you want to do is to use old
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PCs, etc. as diskless thin clients. It works OK on systems with over
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100 thin-client workstations.</P>
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<P>Linux provides NFS (Network File System) so that if ordinary computers
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are connected to each other via a network, then a person on one
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computer can run programs on another computer. Such a program sends
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messages over the network so that it appears just like a program was
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being run by your local computer. But such a program is actually
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being run on another computer on the network. It works also with X
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Window so that one may see GUI images generated on another computer.</P>
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<P>Linux also allows a computer to be diskless and boot over a network.
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See the "Terminal Server Project" above which has special software for
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this purpose. Network-boot-HOWTO gives an overview. Older documents
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are Diskless-HOWTO and Diskless-root-NFS-HOWTO. Thus using a diskless
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computer which runs NFS enables you to run programs on another
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computer (the server). This is just like using a NC (Network
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Computer). It's not really a NC but it's emulating a type of NC.
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It's also often called a "terminal" and in some sense it is.</P>
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<P>Thus if you have an old PC with an ethernet card (NIC) you may be able
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to use it as a NC. One source of info on this is Thinclient-HOWTO.
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Even if your old PC doesn't have a NIC, you could still use it to
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emulate a text-terminal. See
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<A HREF="Text-Terminal-HOWTO-10.html#term_emulation">Terminal Emulation</A>.</P>
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<P>There are also a number of genuine Network Computers (NC) that will
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work with a Linux server. Today some NCs run the Linux OS inside the
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NC. Before Linux became popular, NCs didn't run the Linux OS but
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required some other OS. But even if the NC uses a non-linux OS, it's
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often possible to make it work with a Linux Server. The non-linux OS
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is simply stored as files on the Linux Server. Then when the NC
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starts up it sends a message to the Linux Server asking for the
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non-linux OS files. This non-linux OS is thus sent to the NC over the
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network and the NC boots.</P>
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<P>The Linux Server runs the NFS and X Window both of which must be
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supported by the NC. This enables one to use the NC as if it were an
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X Window terminal.</P>
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<P>There are some Linux HOWTOs for certain brands of NCs:</P>
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<P>
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<UL>
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<LI> JavaStation-HOWTO (by Sun) </LI>
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<LI> NC-HOWTO (IBM NetStation)</LI>
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<LI> NCD HOWTO (NCD-ThinSTAR)</LI>
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<LI> NCD-X-Terminal HOWTO </LI>
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<LI> XDM-and-X-Terminal HOWTO</LI>
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</UL>
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</P>
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<H2><A NAME="ss3.5">3.5</A> <A HREF="Text-Terminal-HOWTO.html#toc3.5">Hardware hookups </A>
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</H2>
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<P> There are 3 different types of hardware arrangements for thin
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clients. The first type just uses a PC computer as a thin client by
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emulating a thin client. It really isn't a thin client but it behaves
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like one. The second type (no longer made ?) looks just like a
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text-terminal. It just looks like a monitor, with a connector for a
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keyboard and another connector for a network cable. It's a dedicated
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thin client and can't be used for anything else. The third type looks
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like a tiny computer. It uses a standard PC monitor and keyboard both
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of which plug into a small box which is a "thin" computer. This box
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provides an interface between the monitor/keyboard and the network.</P>
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<H2><A NAME="ss3.6">3.6</A> <A HREF="Text-Terminal-HOWTO.html#toc3.6">History and the future</A>
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</H2>
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<P> Promoters of NCs and related Window-Terminals projected that they
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would soon replace millions of PCs. In 1998 about .7 million thin
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clients were sold worldwide with (about 27% of them being NCs). In
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1999 it dropped to .6 million but went up to .9 million in 2000 (vs.
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1.3 million predicted). In 2001 it reached 1.09 million with 1.4
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million predicted for 2002.</P>
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<P>Microsoft servers (as of 2003) still dominate the market, but the
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clients may run Linux for which users still have to pay license fee
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for each Linux client to Microsoft. Thus free all-linux systems are
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gaining ground.</P>
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<P>A major reason why growth was not as rapid as predicted is that PCs
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have come down in price in recent years so that they are often not
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much more expensive than a thin client. However, it's argued that
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even though thin clients may cost the same as PCs, the maintenance and
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administration costs are less. Note that thin clients sometimes
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replace text terminals instead of PCs.</P>
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