Port XTender

Port XTender

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Port XTender is a software serial port bridge between Mac OS X's Classic environment and the internal modem that is standard equipment on all shipping Macs.

In Mac OS X, applications which have not been updated to run natively instead run inside the Classic environment. Although Classic is much like a real OS 9 system, it lacks access to low-level hardware such as the internal modem. This poses a problem for applications such as MacAuthorize, which requires the use of a modem but runs in Classic.

Port XTender is a software bridge that allows these applications to use the internal modem.


Contact me if you'd like to try a time-limited, but otherwise fully functional demo of Port XTender.


The price for Port XTender is $100. Please try the demo first and make sure it works before purchasing. After purchase, you'll be sent a license upgrade (56K compressed) by email.

You can purchase Port XTender at Kagi's Internet store.

Again, make sure the demo works before you purchase Port XTender. Some configurations may not work due to modem incompatibilities, and it's your responsibility to verify that Port XTender works (using the demo) before you purchase it. There are no refunds.


Port XTender enables communication between an application running in Classic and the internal modem. Port XTender is not, however, responsible for the content of that communication. It's up to the application (as configured by the user) to send suitable initialization commands to the modem, and up to the modem to implement the command set and behave correctly in general. Some of the more recent Apple modems actually support a reduced command set, and exhibit other problems, like failing to connect to very old modems, or not emitting "NO CARRIER" when a dial attempt fails.

One issue is caused by Mac OS X itself -- when Port XTender requests use of the modem, OS X's Unix layer performs its own modem initialization, leaving the modem in a different state than under OS 9, which causes problems with some old modems. If you get "Host not responding" error messages from MacAuthorize, add "\N1" (without quotes) to the modem initialization string in 'Setup / Communications...'. (This disables attempts to negotiate certain protocols that are confusing the remote modem.)

If you are having issues using Port XTender and can demonstrate that your modem connects to your processor's modem without Port XTender (e.g. in Mac OS 9), I'll be glad to help you track down and fix the problem. Otherwise, I may not be able to help you. You may wish to contact your modem's vendor (i.e. Apple) or your credit card processor for support. Using an alternate phone number may help if there are different modems answering on that line.

You may find Dave Alverson's ZTerm application useful. You can use the Mac OS X version to send commands directly to your modem and observe its behavior (without interference from MacAuthorize or Port XTender), or run the Mac OS 9 version in Classic to also verify that Port XTender is working on your system. If you can establish a connection in ZTerm, then it should be possible to get MacAuthorize working.

Please accompany requests for support with the following information from System Profiler (Apple menu, About This Mac, More Info...):

(Click in the information panel, Select All, and Copy.) Also: