Table of Contents

• Background of VT102 Emulation/Emulators
• VT102 Technical Details and Esc-Squences
• Testing a VT102 via vttest
• ZOC Terminal: Modern VT102 Emulation for Windows and macOS

Background of VT102 Emulation/Emulators

In computing, a DEC VT102 (or DEC VT100, which is nearly the same) is a pretty reliable standard terminal type for access to a variety of computer systems.

VT100 and VT102 were introduced in 1978 by DEC, a former competitor of IBM and maker of computer equipment and mainframe computers. It was originally sold as a physical stand-alone terminal for the VAX mainframes.

In the past (before the PC), a VT100/VT102 terminal was to be a device consisting of a physical screen and keyboard. The terminal was connected to a central server and provided a user with the means to enter data into the server and see results that the server sent back to the user's screen. Thus the users had (rather inexpensive) terminals on their desk to provide them with shared access to a (prohibitively expensive) central computer.

VT102 Technical Details and Esc-Squences

As all terminal types, VT102 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.

The VT102 terminal (or emulator) interprets escape sequences and control codes used by the original terminal, providing a user-friendly interface for accessing remote systems or running text-based programs, preserving compatibility with legacy applications and systems.

For example, 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 ^[1merror^[0m!  to the VT100 or VT102 terminal. Rather than displaying all the text, the VT100 or VT102 terminal will interpret ^[1m  and ^[0m  as commands that tell it to highlight the text that is received between them, so the output would be:
This is an error!.

Here is a list of basic VT102 control codes:

A fulll list of terminal emulation sequences for VT102 can be found in the VT102 User Guide on vt100.net.

Testing a VT102 via vttest

The quality of a terminal emulator can be measured by testing how fully it implements the terminal emulation sequences (see above) and how closely its matches the original terminal's behavior in borderline situations (i.e. when it receives unexpected, faulty or weird combinations of sequences).

Vttest is an application that is used to demonstrate features of VT102 and related terminals, or emulations thereof, such as xterm. The program was originally written in 1986 by Per Lindberg.

ZOC has been tested using the vttest suite, based on a test score developed by Columbia University. ZOC Terminal has scored an excellent 105 Points (see the full report), which ranks it among the best in the industry.

ZOC Terminal: Modern VT102 Emulation for Windows and macOS

Today most 'terminals' are simply a software running on a PC. But many standard telnet clients can be used to emulate VT102 terminals in a basic way, but lack support for certain subtleties in the way true VT102 terminals handled the incoming data. Essentially, the basics of VT102 are easy to implement, which is why it is supported in most terminal software to some extent, but the subtleties are hard to get right.

ZOC however is different, it lets you access mainframes via a telnet or SSL/SSH v2 connection using an expertly built VT102 emulation. Additionally ZOC supports a wide scale of other emulations used in the Unix world, like Linux, xterm, VT220, Wyse, QNX, etc.

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. All these are offered in solid implementations that leave nothing to be desired.

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