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Overview: Servers are central computers that can be located anywhere in the world. To use or maintain them, they need to be accessed through so-called dumb terminals or thin clients or PCs running a terminal emulation, e.g. VT220 or xterm.
The xterm terminal emulation originates in the Unix X-Windows graphical session manager on computers running the Linux operating system. But xterm terminal emulation software is also available on Windows or macOS, so you can actually access a server from a regular computer running Windows or macOS.
The term xterm actually has to meanings. It both describes the actual program named xterm (the original terminal emulator from the X-Windows package), but also a technical standard that describes control codes that let a server control the display of text on a terminal.
In computing, xterm is the standard terminal emulator for the X Window System. A user can have many different invocations of xterm running at once on the same display, each of which provides independent input/output and each in fact simulating a physical standalone terminal.
Xterm originated prior to the X Window System. It was originally written as a stand-alone terminal emulator program for the VAXStation 100 (VS100) by Mark Vandevoorde.
As all terminal emulations, xterm is a standard that allows the server to send text to the user's screen. By embedding special controls in the text, rather than just displaying text from left to right and top to bottom, these codes also allow control over the placement and display charachacteristics (location, color, etc.) of the text.
Xterm extends the possibilities of earlier terminal emulation definitions like DEC VT100 or VT220 to allow the server to control special characteristics that go beyond the requirements of physical terminals, like the placement of the xterm terminal window on the user's screen or setting the title which is displayed in the xterm window. xterm terminals also allow the server to interact with the user's mouse.
As all terminal types, xterm is a standard that allows the server to send text to the user's screen. By embedding special controls in the text, these codes allow control over the placement and display charachacteristics (location, color, etc.) of the text, rather than merely displaying text from left to right and top to bottom like an old teletype (TTY).
E.g. in order to send the text "this is an error!" to the user's screen with the word "error" highlighted, the host would send This is an ^[1m error ^[0m! to the xterm terminal. Rather than displaying all the text, the xterm terminal will interpret ^[1m and ^[0m as commands that tell it to highlight the text that is received between them.
While the above code actually also works in some (but not all) other terminal types, like VT100 or VT220 (xterm controls are actually a superset of these), xterm vastly expands the codes and possibilites over those.
Notably, xterm is one of the few terminals, that acknowledges the fact that it lives in an emulator and is not a physical terminal (see terminal emulator) and thus includes codes that manipulate the emulator window itself.
Here is an exceprt from one of the code squences that allow that:
Another improvement in the xterm terminal emulation is the strict definition of function keys and the codes sent by the terminal, especially in combination with combinations of keyboard modifier keys like shift, alt, ctrl.
A fulll list of terminal emulation sequences for xterm can be found on xfree86.org.
Today most 'terminals' are simply a software running on a PC. But many standard telnet clients can't be used to emulate xterm terminals properly, because the xterm protocol is rather powerful and full of subtle details which are hard to get right.
ZOC Terminal however is different and lets you access servers via a telnet or SSL/SSH connection using the Xterm emulation in a consistent and industrial strength quality implementation.
Additionally ZOC supports a wide scale of other emulations used in the Unix world, like VT220, Linuxterm, but also emulations that were used with other operating systems, like Wyse, TN3270, Televideo and others.
The ZOC telnet/SSH client also includes a number of other useful features. It comes with a modern multi-tabbed user interface and is highly configurable. Beyond that it includes the usual terminal features such as keyboard redefinition and scroll back buffer. It also has some very advanced and unique features such as a powerful script language and automatic triggering of actions based on received or typed text. This terminal emulation software also supports vt102, vt220 and several types of ansi as well as Wyse, TVI, and Sun's CDE. ZOC also features major file transfer protocols like X-, Y- and Zmodem as well as Kermit and others. All these are offered in solid implementations that leave nothing to be desired.