tn3270 for the Macintosh
by Peter DiCamillo

What's new — October, 2019

What's new — November, 2013

What is tn3270?

Tn3270 is a terminal emulation program for connecting to computers which use IBM 3270 terminals. Major features of the emulation include color, extended highlighting, support for different screen and font sizes, and SSL support. Some more obscure features include support for the APL character set, and support for file transfer and remote printing when tn3270 is used with an IBM VM/CMS host. The Classic version of tn3270 also supports 3179 graphics emulation.

There is no license fee for either commercial or non-commercial use of the tn3270 application. The tn3270 source code is freely-licensed for non-commercial use, but must be licensed for commercial use.

What is required to use tn3270?

To use tn3270, the host computer must provide a telnet server which supports the extensions for 3270 terminals. On your Macintosh, you must be able to connect to the host server using TCP/IP.

Although primarily a 3270 emulation program, tn3270 also supports ordinary line mode telnet connections. This support allows tn3270 to operate with hosts which establish a line mode connection before entering 3270 mode, as well as with line mode only hosts. When operating in line mode, tn3270 emulates a DEC VT52 terminal.


  1. All versions of tn3270 X support the original 3270 extensions to telnet. The newer tn3270e protocol is supported as an experimental addition to version 3.4.0.
  2. Tn3270 may be used with hosts which support IBM 5250 terminals. However, not all 5250 functions will be available.

Which Macintosh operating systems are supported?

The latest version of tn3270 X, 3.4.0, is supported on Mac OS X 10.3.9 Panther through macOS 10.14 Mojave. Older versions of tn3270 X are available for use with OS X 10.1.5 and later, as listed under the downloads. The Classic version of tn3270, 2.5b5, is compatible with classic Mac OS versions.

Will tn3270 X support macOS 10.15 Catalina?

macOS 10.15 Catalina is the first version of macOS which does not support the use of 32-bit applications. Many older applications, including tn3270 X, are 32-bit applications, and must be updated to the 64-bit model for Catalina. Unfortunately, this won't be possible for tn3270 X. Tn3270 X was developed using Apple's Carbon framework, which was originally provided for porting classic Mac applications to OS X. When 64-bit support was being introduced into OS X, Apple made a decision to not support 64-bit Carbon applications. As a result, it's not feasible to update tn3270 X to 64 bits. The only solution would be a rewrite of the application, and there are no current plans for a rewrite. Users of tn3270 X are encouraged to use the macintosh-tn3270 mailing list to discuss alternatives to tn3270 X for Catalina. If you are a developer who would be interested in participating in an open-source project to implement a replacement for tn3270 X, please contact Peter DiCamillo.

Download the Latest Version of tn3270

Version 3.4.0 is an update to version 3.3 that adds support for OS X 10.9 Mavericks. It has also been tested successfully with OS X 10.10 Yosemite through macOS 10.14 Mojave. Besides supporting the latest versions of OS X, it also includes experiment support for the tn3270e protocol and for client SSL certificates. See the release notes for more information.

Download Previous Versions of tn3270
Read the Latest tn3270 Release Notes

tn3270 X 3.4.0 Release Notes, November 9, 2013
  PDF format
  RTF format

Archives for tn3270

The tn3270 archive site contains current and older versions of tn3270, source code for the Classic version, and other tn3270-related files. Source code for tn3270 X is not currently included in the archives, but is available from the author upon request.

Joining the tn3270 Mailing List

A tn3270 mailing list, macintosh-tn3270, is available for discussing tn3270. It is also used for announcements of new test and final releases. To join or search the list archives, go to the macintosh-tn3270 list web page.


tn3270 for the Macintosh was written by Peter DiCamillo. It includes code written by Greg Minshall to support the tn3270 telnet protocol, Copyright © 1984-1988 by the Regents of the University of California and by Gregory Glenn Minshall.

Development of the Classic version of tn3270 was supported by Computing and Information Services at Brown University. Also, the Classic version includes the NCSA TCP/IP Kernel for the Macintosh, written by Tim Krauskopf and Gaige B. Paulsen, Copyright © 1987-1988 by the Board of Trustees of the University of Illinois.

The icons for tn3270 were done by Steve Klingsporn.

The original version of this web page was contributed by Andrew Starr.

tn3270 for the Macintosh Classic version Copyright © 1988-1996 by Brown University and by Peter DiCamillo. OS X version Copyright © 2002-2006 by Peter DiCamillo.

Updated October 10, 2019