| 210/230 | 7.1 | PowerBook | 1.0 thru 1.1.2 | System Enabler 201 |
| PowerBook Setup | 1.0 thru 1.1.2 | PowerBook Duo 1.0 | ||
| Express Modem | 1.5 thru 1.5.2 | System Enabler 201 | ||
| Express Modem | 1.5 thru 1.5.2 | PowerBook Duo 1.0 | ||
| 250/270c | 7.1 | PowerBook Setup | 1.0 thru 1.1.2 | PowerBook Duo 1.0 |
| Express Modem | 1.5 thru 1.5.2 | PowerBook Duo 1.0 | ||
| 280/280c | 7.1.1 | Express Modem | 1.5 thru 1.5.2 | PowerBook Duo 2.0 |
The Express Modem releases did not have any effect on this issue before release 1.5, which ships with the Duo 280/280c. With release 1.5 of the Express Modem, the choice for the modem now is contained in the "Express Modem" control panel rather than the "PowerBook" or "PowerBook Setup" control panel. Express Modem releases 1.0 through 1.1.2 did not contain the ability to choose the modem.
The following is a list of the Duos, and the Enabler that originally shipped with them:
* Duo 210/230 -- System Enabler 201
* Duo 250/270c -- PowerBook Duo Enabler 1.0
* Duo 280/280c -- PowerBook Duo Enabler 2.0
For a Duo with System Enabler 201 installed, the "PowerBook" control panel contains the ability to choose either the "Internal" or "External" Modem. This is true for the Express Modem releases from 1.0 through 1.1.2, and with the "PowerBook" control panel releases 7.1.1 through 7.1.3.
For a Duo with the PowerBook Duo Enabler 1.0 installed, the "PowerBook Setup" control panel contains the ability to switch the modem choice. The choices are "Compatible" or "Normal". Compatible refers to Internal, and Normal to External. These Duos usually shipped with Express Modem 1.1.2, and release 7.2 of the "PowerBook" and "PowerBook Setup" control panels.
For a Duo with the PowerBook Duo Enabler 2.0, the choice for the modem now is contained in the "Express Modem" control panel rather than the "PowerBook" or "PowerBook Setup" control panels. "Express Modem Settings" needs to be selected from the pop-up menu, and then "Use Express Modem" or "Use External Modem" can be chosen. Duos which come with this Enabler installed, also come with Express Modem 1.5. As shipped, the release of the PowerBook control panel is 7.3.1 and of the PowerBook Setup is 7.3.
Complicated as this is, it obviously gets more interesting when the user upgrades the Enabler via system software, the Express Modem software, or both. For the purposes of this answer, I will address only the changes that occur when the Express Modem software is upgraded while the Enabler/system software remains the same.
From a Duo with the System Enabler 201, when the Express Modem 1.5 (or 1.5.1 or 1.5.2) is installed, the way to choose the modem moves from the "PowerBook" control panel to the "Express Modem" control panel. In the Express Modem control panel, "Express Modem Settings" must be selected to actually allow selection of the "Use Express Modem" or "Use External Modem" option.
For a Duo with the PowerBook Duo Enabler 1.0 installed, upgrading the Express Modem software to 1.5 (or 1.5.1 or 1.5.2) changes the way to choose the modem from the "PowerBook Setup" control panel to the "Express Modem" control panel. And again, in the Express Modem control panel, "Express Modem Settings" must be selected to actually allow selection of the "Use Express Modem" or "Use External Modem" option.
In other words, as of release 1.5 of the Express Modem software, control of the selection of internal/external modem moved from the Duo's PowerBook/PowerBook Setup control panels to the Express Modem's control panel.