Terminal emulator

A terminal emulator, or terminal application, is a computer program that emulates a video terminal within another display architecture. Though typically synonymous with a shell or text terminal, the term terminal covers all remote terminals, including graphical interfaces. A terminal emulator inside a graphical user interface is often called a terminal window.

A terminal window allows the user access to a text terminal and all its applications such as command-line interfaces (CLI) and text user interface (TUI) applications. These may be running either on the same machine or on a different one via telnet, ssh, dial-up, or over a direct serial connection. On Unix-like operating systems, it is common to have one or more terminal windows connected to the local machine.

Terminals usually support a set of escape sequences for controlling color, cursor position, etc. Examples include the family of terminal control sequence standards that includes ECMA-48, ANSI X3.64, and ISO/IEC 6429.

In the early days of computing, with the advent of interactive computing, the prevailing model involved a central computer connected to multiple terminals. This configuration, known as the centralized or mainframe model, featured a powerful central computer that performed all the processing tasks, while terminals served as input/output devices for users to interact with the system. These systems were initially character based.

A character-oriented terminal is a type of computer terminal that communicates with its host one character at a time, as opposed to a block-oriented terminal that communicates in blocks of data. It is the most common type of data terminal, because it is easy to implement and program. Connection to the mainframe computer or terminal server is achieved via RS-232 serial links, Ethernet or other proprietary protocols.

When personal computers became ubiquitous in the 1980s, they offered the option of running software on the user's personal computer, providing an opportunity to replace the expensive and space consuming hardware terminals with something that had additional functions. Immediately software became available, that could emulate the functions of the hardware terminals on a PC. Examples of such software for DOS were Telix or Telemate, which was published in 1988 and could emulate a DEC VT102 terminal.DEC VT102

Workstations, usually running versions of Unix, also became common in the 1980s. Unix systems usually provided access to the command line with locally-attached or dial-up terminals. Unix workstations were designed to be used primarily through a graphical user interface (GUI); to provide access to the command line, the GUI included terminal emulator applications that behaved like locally-attached terminals.

During the 1990s, new operating systems like Windows and OS/2 arrived, providing the technical background for more terminal emulators like Telix for Windows, ZOC for OS/2, or PuTTY, which was initially released for Windows in 1998 and which (together with its derivates) remains a very popular choice to this day.