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LDP/howto/linuxdoc/Text-Terminal-HOWTO.sgml
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@ -1,11 +1,14 @@
<!doctype linuxdoc system>
<article>
<title> Text-Terminal-HOWTO </title>
<title> Text-Terminal-HOWTO
<author> David S. Lawyer <url url="mailto:dave@lafn.org">
<date> v1.15, October 2000
<date> v1.16, October 2000
<!--
Change log:
v1.16 October 2000 Thin clients+; NC Howtos; Correction of bad typo
"text terminals are fully obsolete". Meant to say "not fully
obsolete". typo Unbounded => Boundless "' )
v1.15 October 2000 Thin Clients; some broken url's changed or deleted
v1.14 October 2000 Suse distribution uses /etc/securetty (didn't
formerly), url of terminfo source, Serial Terminal Linux, pseudo
@ -144,9 +147,10 @@ sites see: <url url="http://linuxdoc.org/mirrors.html">.
Various formats are available. If you only want to quickly check the
date of the latest version look at <url
url="http://linuxdoc.org/HOWTO/Text-Terminal-HOWTO.html">. The
version your are currently reading is: v1.15, October 2000 . New in this version
is: Thin Clients; some broken url's changed or
deleted.
version your are currently reading is: v1.16, October 2000 . New in this version
is: Thin-clients+; NC Howtos; Correction of bad typo "text
terminals are fully obsolete". Meant to say "not fully obsolete".
typo Unbounded => Boundless;
<sect1> Related HOWTO's <label id="related_howtos">
<p> Go to the websites shown above to get these.
@ -154,9 +158,13 @@ deleted.
<item> Serial-HOWTO has info on Multiport Serial Cards used for both
terminals and banks of modems. It has general technical info on the
serial port including troubleshooting it.
<item> MacTerminal mini-HOWTO
<item> Modem-HOWTO
<item> Serial-Programming-HOWTO
<item> NC mini-HOWTO
<item> NCD-X-Terminal mini-HOWTO
<item> NCD-HOWTO
<item> Thinclient-HOWTO
<item> Xterminal-HOWTO (unmaintained). It's at <url url=
"http://sunsite.unc.edu/pub/Linux/docs/HOWTO/unmaintained/mini/Xterminal">
</itemize>
@ -257,9 +265,10 @@ server, etc.
Other names for text terminals are "serial terminal", "character-cell
terminal", "ASCII/ANSI terminal", "asynchronous terminal", "data
terminal", "video terminal" and "video display terminal" (VDT). In
olden days "video display unit" (VDU) was used for terminals but
strictly speaking, it excludes the keyboard.
terminal", "video terminal" and "video display terminal" (VDT) and
"green terminal" (since many used green displays). In olden days
"video display unit" (VDU) was used for terminals but strictly
speaking, it excludes the keyboard.
"Block mode" was used exclusively by old IBM mainframe terminals but
many modern terminals also have this capability (which is not used
@ -283,22 +292,10 @@ display images. One may form arrows <--- and draw boxes with _ and
|. With special graphic character sets, even more is possible. By
using all the letters, one may produce "ascii graphics" art. The term
"graphics terminal" usually means a terminal that can display bit
mapped images. However, this term is sometimes applied to all
mapped images. However, this term is sometimes applied also to
text-only terminals since text is a limited form of graphics. <label
id="vector_graphics">
<sect1> Thin Clients (Terminals ?)
<p> These are either terminals or thin (minimal) computers. In
contrast to text-terminals, they all display a high-speed GUI. They
are dependent on higher power computers (servers) for their operation.
For a true 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 client but some things such as administration,
still depend on the server. Since the client here is not "thin" it's
not clear that this is really a thin client. Some claim that
text-terminals are also thin clients.
<sect2> Graphics Displays
<p> There are two basic types of graphics displays: raster and vector
(rarely used). Raster graphics (bit-mapped) puts dots on the screen
@ -308,74 +305,136 @@ intended to be used for monochrome screens that don't have any dots.
They use smart electronics to draw lines and curves with an electron
beam that can move in any direction (at any angle and location). True
vector graphics draws high quality lines without zig-zags but is both
rare and expensive. Raster graphics is almost universally used today.
For PC's, images encoded in vector graphic format are sometimes used
but they are translated to raster graphics format for display (with a
drop in image quality).
rare and expensive. Raster graphics is almost universally used today
for both PCs and text terminals. For PC's, images encoded in vector
graphic format are sometimes used but they are translated to raster
graphics format for display (with a drop in image quality).
<sect2> Full Graphics Terminals (often known by other names)
<p> None of these are covered in this document. A terminal that
deserves to be called smart is a graphics terminal which can rapidly
display full-screen graphics just like a PC monitor. It will also
have a mouse. Bytes sent to it often represent bit-maps for pictures
(and other graphics). It will often use a high-speed connection to
its host computer using twisted pair or coax cable. X-Window
terminals are such devices. See the link to Xterminal-HOWTO at <ref
id="related_howtos" name="Related HOWTO's">. So are some "thin
clients" including ones which have a MS-Windows GUI which comes from a
remote Windows Terminal Server.
<sect1> Thin Clients (Terminals ?)
<sect2> Introduction
<p> These are thin (minimal) computers that behave something like
terminals. Since text terminals (except for very old one) 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
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 client but some things such as administration, still depend on
the server. Since such a client is not really "thin" it's a misnomer
to call it a "thin 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.
Thus a thin client is like a terminal and perhaps should be called a
terminal. The thin client 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, often twisted pair
(UTP). 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 two major types of thin clients (and some additional types as
well which will not be discussed here). One type is the "Window
Terminal" which usually runs under MS software and servers. The other
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.
<sect2> Window Terminals
<p> These can run under MS Windows NT/2000 using a proprietary protocol.
They are true terminals since all the computing work is done by the
server running Windows. They are also called "Window-based Terminals"
(WBT). Some have support for unix-like systems as well and may not
claim to be WBTs (even though they can be used as WBTs). They are
something like computers since they run an operating system (often
stored in flash memory so it may be updated). Some can support
X-Windows also and can be used for Linux (from a Linux server). Many
so called "network computers" can also run X-Windows. This will be
discussed in the next section.
For displaying the MS-Windows GUI, Citrix was (and is) a major player
with what was called Winterm using it's WinFrame software (which
supported Windows 3.1). Microsoft licensed some of this and then came
out with Hydra (code name), also known as "Windows Terminal Server".
It works with versions 4 or higher of MS Windows NT. Then other
companies that had their own proprietary systems decided to support
Microsoft's system.
companies that had their own proprietary systems for MS Windows
decided to support Microsoft's system.
Citrix uses its ICA protocol and has created an add-on to Hydra known
as pICAsso so that WinFrame (ICA) based terminals can use the Hydra
system. There exits a Linux ICA client. Microsoft has substituted
RDP (Remote Desktop Protocol) for ICA. Citrix has replaced WinFrame
with MetaFrame which supports Windows 95 and is used in conjunction
with "Windows NT Terminal Server Edition". There is also the
"MultiConsole Personal Terminal" by Unbounded Technologies. Tektronix
had its own multi-user interface but will now support Hydra.
system. There exits a ICA client that internally runs Linux (but
connects to a MS Window's server). Microsoft has substituted RDP
(Remote Desktop Protocol) for ICA. Citrix has replaced WinFrame with
MetaFrame which supports Windows 95, etc. and is used in conjunction
with "Windows NT Terminal Server Edition".
The above is sometimes called "network computing" since the terminals
and servers connect to each other over a network. Network computers
are something different as described below.
may be somewhat different as described below.
<sect2> Network Computers (NCs)
<p>These are neither true computers nor terminals but are something
in-between. They are also a type of thin client. One type of network
computer (NC's) is a computer with a CPU but no hard Disk. They are
full-graphics and connect to a server computer. They are different
from terminals since the programs they run execute on their own CPU
chips. Java code may be sent to them for execution. IBM calls this a
"Network Station". They should work on IP networks and might work
under a server running Linux. Wintel established a "NetPC" which,
unlike the above, is almost a PC computer. However, it has no
removable disks so users can't install their own software or obtain
copies of anything.
<p>These are neither true computers nor true terminals but are
something in-between. One type of network computer (NC's) is a
computer with a CPU but no hard Disk. The OS it needs to run is sent
to it over a network. NCs are full-graphics and use the services of a
server computer. They are a little different from terminals since
some of the programs they run may execute on their own CPU chips.
Running a browser was supposed to be one of their primary functions
and thus Java code applets may be sent to them for execution. Many
NCs support X-Windows so that one may use a Linux server to support
it. IBM called their NC a "NetStation" but now calls it "NetVista".
They should work on Intranet type networks and NetVista even runs the
the Linux OS.
Wintel came out with a "NetPC" which, unlike the above, is almost a PC
computer. However, it has no removable disks so users can't install
their own software or obtain copies of anything.
<sect2> Thin Clients Under Linux
<p> Linux provides NFS (Network File System) so that if ordinary
computers (not thin clients) are connected to each other via a
network, then a person on one computer can run programs on another
computer. It works also with X-Windows so that one may see GUI images
generated on another computer. Linux also allows a computer to be
diskless (see Diskless-HOWTO) and boot over a network. Thus using a
diskless computer which runs NFS is just like using a NC (Network
computers are connected to each other via a network, then a person on
one computer can run programs on another computer. Such a program
sends messages to you over the network so that it appears just like the
program was being run by your local computer. It works also
with X-Windows so that one may see GUI images generated on another
computer. Linux also allows a computer to be diskless (see
Diskless-HOWTO) and boot over a network. Thus using a diskless
computer which runs NFS enables you to run programs on another
computer (the server). This is just like using a NC (Network
Computer). It's not really a NC but it's emulating a type of NC.
It's also sometimes referred to (incorrectly ?) as a "terminal".
It's also often called a "terminal" and in some sense it is.
Thus if you have an old PC with an ethernet card (NIC) you may be able
to use it as a NC. Even if it doesn't have a NIC, you could use it as
a text-terminal. See <ref id="term_emulation" name="Terminal
Emulation">. So Linux too supports a type of thin client which is the
subject of Thinclient-HOWTO. For using the Sun JavaStation NC under
Linux see the JavaStation-HOWTO.
to use it as a NC. The details of this are covered in
Thinclient-HOWTO. Even if your old PC doesn't have a NIC, you could
still use it as a text-terminal. See <ref id="term_emulation"
name="Terminal Emulation">.
There are also a number of genuine Network Computers (NC) that will
work with a Linux server. Today some NCs run the Linux OS inside the
NC. Before Linux became popular, NCs didn't run the Linux OS but
required some other OS. But even if the NC needs a non-linux OS, it's
often possible to make it work with a Linux Server. The non-linux OS
is simply stored as files on the Linux Server. Then when the NC
starts up it sends a message to the Linux Server asking for the
non-linux OS files. This non-linux OS is thus sent to the NC over the
network and the NC boots.
The Linux Server runs the NFS and X-Windows both of which must be
supported by the NC. This enables one to use the NC as if it were an
X-Window terminal.
There are some HOWTOs for certain brands of NCs:
<itemize>
<item> JavaStation-HOWTO (by Sun)
<item> NC-HOWTO (IBM NetStation)
<item> NCD mini-HOWTO (NCD-ThinSTAR)
<item> NCD-X-Terminal mini-HOWTO
</itemize>
<sect2> Hardware hookups
<p> There are 3 different hardware arrangements for thin clients.
@ -548,23 +607,19 @@ and send e-mail to each other. It's similar to a local network.
<sect1> Are Text Terminals Obsolete ?
<p> Text terminals are technologically obsolete because for a slightly
higher cost of hardware, one could build a smart terminal (with the
higher cost of hardware, one could build a smarter terminal (with the
same quality of display). This wasn't always the case since around
1980 memory cost thousands of dollars per megabyte. Today with low
costs for memory and processors, one could make a text terminal smart
for only about a 10% or 20% increase in hardware cost.
costs for memory and processors, one could turn a text terminal into a
GUI graphic terminal for only about a 10% or 20% increase in hardware
cost.
The reasons that text terminals are fully obsolete are:
The reasons that text terminals are not fully obsolete are:
<itemize>
<item> There is no satisfactory standard interface for smart graphics
terminals that can be used with Linux (but there is for MS Windows).
However one can run a diskless PC under Linux on a network where the
diskless PC is a substitute for a smart graphics terminal.
<item> The resolution of characters on the screen is better on
monochrome terminals than for monitors in text mode.
<item> Many people don't need full screen graphics.
<item> Text terminals are low in cost and allegedly take longer to
become obsolete, yet can give access to a much newer (and powerful)
computer.
<item> Since running a text-terminal (in contrast to a full-graphics
<item> Since running a text-terminal (in contrast to a GUI-graphics
terminal) doesn't consume much of a modern PC's resources, a large
number of terminals may be efficiently run from one PC.
</itemize>
@ -3426,6 +3481,9 @@ become a serial guru. Most of the defaults should work OK and some of
the settings are needed only for certain obsolete dumb terminals made
in the 1970's.
<tt/stty/ is documented in the man pages with a more detailed account
in the info pages. Type <tt>"man stty"</tt> or <tt>"info stty"</tt>.
Whereas <tt/setserial/ only deals with actual serial ports, stty is
used both for serial ports and for virtual terminals such as the standard
Linux text interface at a PC monitor. For the PC monitor, many of the