| VT220 Emulation uses the telnet protocol to create a | | | | One feature that is available with VT220 emulation is |
| TCP/IP connection to a remote host typically running | | | | the answer back message. The answer back |
| the Unix, AIX, IBM i or Linux operating system. | | | | message initiates a question and answer progression |
| Originally, video terminals were used to communicate | | | | between the PC and the host system. This feature |
| with these systems. The most established | | | | can be used to pass the identity of the PC to the |
| manufacturer of VT terminals was Digital Equipment | | | | host system without user interaction. Hexadecimal |
| Corporation (DEC). The first of these types of | | | | values can be used to include function keys in the |
| terminals was the VT05, released in 1970. | | | | answer back message. For example, to send the |
| As time progressed and VT emulation gained in | | | | enter key (^M), use the hexadecimal equivalent of |
| popularity, other manufacturers began producing | | | | ^M preceded by the ~ character, which would be |
| video terminals to compete with the DEC VT05. The | | | | ~0D. |
| result was a splintered market with a multitude of | | | | Another feature that can be used with VT220 |
| terminals each using a proprietary set of escape | | | | emulation is local echo. With local echo enabled |
| sequences to communicate with the host system. | | | | through the terminal emulator, each keyboard |
| User frustration with functional inconsistencies and | | | | command that is entered is echoed back on the |
| system incompatibility resulted in the development of | | | | display screen. For example, if a user typed p3, pp33 |
| the ANSI device control standard. The first DEC | | | | would be displayed on the screen. The first instance |
| terminal to support the ANSI standard was the | | | | of "p" would be the "p" that the user typed, and the |
| VT100. The DEC VT220 terminal was introduced to | | | | second instance is the "p" returned by the host. Local |
| the market in 1983, and included an extended | | | | echo can be used for diagnostic purposes. |
| keyboard and the ability to redefine display | | | | Most terminal emulators will also allow users to |
| characters. It was followed by releases of the widely | | | | configure a scroll back buffer. With the scroll back |
| used VT320 and VT420 terminals that included | | | | buffer configured, the user can scroll back up the |
| graphics support. | | | | screen the specified number of lines to previously |
| By the late 1980's, PC use had gained a considerable | | | | issued commands. Some terminal emulators also allow |
| foothold within business organizations. Users now | | | | users to configure the speed with which the |
| needed a way to communicate with mainframes | | | | buffered data will scroll across the screen. |
| from their desktops without the need for a separate | | | | VT220 emulation is often used to access IBM pSeries |
| display terminal. Terminal emulation software was | | | | or System P servers. This line of servers was |
| developed to fill this need. Using VT220 emulation, | | | | originally named RS/6000, eventually became the IBM |
| users who had previously operated a DEC VT220 | | | | pSeries line, and has now been replaced by IBM |
| terminal for accessing their host system remotely, | | | | PowerT Systems. Using VT220 emulation in |
| could access it from their desktop PC instead. | | | | conjunction with these servers from IBM offers |
| VT220 emulation supports both 7-bit and 8-bit coded | | | | virtualization, consolidation and energy management |
| character sets. The 7-bit character set consists of | | | | technologies that can significantly reduce the costs |
| the first 128 ASCII characters only. The 8-bit | | | | associated with enterprise data and application |
| character extends the 7-bit set by accommodating | | | | management. |
| additional multinational and graphical characters. | | | | |