Terminal emulator

A terminal emulation is a computer program that simulates the function of a terminal. Terminal emulations can be displayed using on personal computer in a window or at a terminal the whole screen area.

The user interface is mostly text-oriented. By escape sequences the character encoding can be switched and thus also graphical symbols are displayed.

The platform on which the emulation takes place, so it must offer at least the possibility of output and input of characters ( eg, ASCII). The platform most commonly used is a graphical user interface. A terminal emulator is used today to use old text-based programs with a newer graphical user interface can, or for new programs that waive graphical Ein-/Ausgabe.

Text application ↔ ↔ terminal emulation graphical interface      ↔ ↔ X11 xterm shell

Architecture

A terminal emulation allows interaction with a text-based program within a graphical user interface. It makes working with programs available that do not directly use the graphic interface for output ( eg, because they have been programmed, when there was no graphical interface for the hardware used, or because it is easier to handle issues via the text interface). The text-oriented program presents it as a text terminal is ( hence the name), and the graphical interface as graphics-capable program.

Operation

A terminal emulator accepts the same task, accomplish the hardware of a terminal and the associated therewith on the mainframe software. However, emulation is a normal process of the operating system that is executed by the CPU of the PC instead of a program stored in the ROM of the host and executed by the CPU. The output of a text-oriented program is analyzed by the terminal emulation and (eg X11) implemented in operations of a graphical interface.

Keystrokes in the terminal window are thereby sent to the process that is executed within the emulation. This is usually a command line interpreter. The command line interpreter is tricked by a pseudo terminal to be connected to a terminal, the master side of the pseudo-terminal is associated with the process of terminal emulation, rather than for example with a serial interface.

Examples

Programs that require a local connection to the mainframe:

• Xterm, rxvt, aterm, Eterm, wterm, Gnome Terminal, console in the Unix world
• "Extra" in the Windows environment for the emulation of IBM terminals
• VTerm and others in the VAX - world
• TeemTalk (available for Linux, Windows CE, XPe)

Programs that are intended for remote access:

• HyperTerminal (included in older Windows operating systems )
• PuTTY (for Windows and Unix -like systems )
• Telnet clients

History, meaning, purpose, perspective

A terminal emulator is a computer program that a computer connected to a mainframe computer, " intelligent" computer can alternatively act as a terminal. For the mainframe, it represents only one data terminal without its own intelligence dar. The replacement may be purely relate in the simple case of the text functionality, but can also replace the graphics capabilities of graphical terminals in the complex case.

Important terminals on larger star-shaped wired computer systems were the 3270 series and IBM in the midrange computer, the VT DEC. The initially expensive PCs were first used meaningfully only in the additional benefits as terminals on larger computers, including to save space, and to locally transfer on the PC changed data and programs on the big computer. For this, the terminal emulation programs were provided on the pure terminal - replacement function with some additional functions beyond to accomplish this data transfer in both directions, ie to push data to the mainframe ( upload), or going to come from him data (download).

Concrete examples: the "simple" DEC terminals were the VT52 and VT100 (VT = video terminal, exposed terminal ). These terminals allowed " only " alphanumeric command dialog and data input and output. With a supplementary character set in the terminal, could be switched by command sequence from the computer to the, it was then possible to use a simple " square graphics " ( similar to the popular Pacman game ) to use. Even the newer terminals VT200 and VT220 did not allow full-screen pixel graphics, but they allowed to load any fonts in the terminal.

The first "real" graphics terminals from DEC were the VT240 ( monochrome, yellow or green letters and pixels) and the VT241. Parallel Sets with advanced graphics capabilities of PCs then subjected to the manufacturers of terminal emulation programs by: The first programs made ​​it possible to replace the PC with a VT52 or VT100. With the Hercules graphics and the VGA standard then advanced, also initially more expensive programs have been sold, which enabled the PC, in addition to imitate a graphics-capable VT240 or VT241. In particular terminalemulierende computers were a problem the provider pure graphics terminals, such as Tektronix. With ever larger screens (XGA standard, 1024 × 768 points, or then 1280x1024 pixels), 17 " - and 19" monitors, the big " dumb" terminals became extinct.

1985 the cost of a graphics station for the DEC VAX -based CAD system MEDUSA approximately 145,000 DM, with a 19 "screen, an input tray and an alpha screen for the command dialog Note: . A graphic station " " was stupid, still the "intelligence" of the connected cable VAX computer additionally required, their computing power for several stations cost proportionately again of similar magnitude, thus causing approximately 300,000 DM total cost of running a single job. This was the time when the well-paid technicians and engineers went back to shift work to use about 16 hours a day these expensive facilities in two layers in order to utilize the better.

With the advent of ever cheaper computers and the appropriate software (eg AutoCAD) such expensive stations and systems had fewer opportunities in the market.

As the prices of PCs always continued to fall, gradually disappeared, the real terminals from the scene. Nowadays rarely pure terminals for user interaction are still used in the workplace. The now well-known, pure terminals in the literal sense as " terminals " of the data processing are used for special functions such as POS systems and automated teller machines.

In addition to the emulation software electronic transfer functionality in hardware on the PC usually still needed, so to present themselves via an interface and a cable connection electrically identical to a terminal. In the early days it was mainly the serial interface ( for VT emulation) or a special plug-in card for IBM connection via coaxial cable.

Nowadays terminal emulations exist mostly as add-on software in PC networks to the often still existing mainframe systems to be able to address ( in addition to the PC uses) nor in addition to benefits. The main purpose, however, is shifting more and more to the networked computing systems themselves, or client-server systems, such as SAP R / 3 and the like.

The use of terminal emulation in the administration of devices without their own user interfaces ( routers, switches, ... ) will also remain valid.

Terminal emulations thus represent a component of the transition from the star-shaped mainframe technology to networked computer networks dar.