3 buttons support does exist in MS-Dos, but it seems like an obscur puzzle which may turn into an headache.
One example is : "When the mouse first gets power, if the left button is held down it switches into Mouse Systems mode. A simple fact, but not always publicised."
Here : Switching a Mouse to 3-Button Mode

Other example is Msinput.ini configuration.
Check this : MS-DOS Mouse Driver Does Not Use Primary Mouse Button Setting

• x=1 sets the left mouse button
• x=2 sets the middle (wheel) button
• x=3 sets the right mouse button

I can hardly believe it, I could never get Microsoft's drivers supports those 3 buttons.
Only CTmouse.exe and Logitech mouse.exe were good.

John Allen Mills wrote on 2025-04-10, 17:04:

As far as I'm aware dosbox emulates a 3-button, PS/2, mouse.

Sure about this ?

My experience is : with some mices, some drivers, some protocol you can get 3 buttons workings in games on a DOS 6.22 real machine.

I looked into it, fairly recently, through DOSBox source code and the MS-DOS Mouse Driver programmer reference book. It's a little bit confusing, but:

* The IBM PC didn't have a third mouse button until the mouse wheel appeared.
* MS-DOS does not support it.
* Many games and programs (Windows 3.X among them) don't support it, and could crash if three buttons are reported the the DOS mouse driver.
* CuteMouse added extensions to the protocol of the DOS mouse driver to support the wheel / third mouse button, but they are unique to it.

But it's only a brief look into it. YMMV.

As a guy who did quite huge rework of mouse support in one of the DOSBox forks, I can tell you:

* 3rd button was present on some mice even in the early 80s (search for the Mouse Systems mouse).
* Some 3rd party DOS mouse drivers did support the 3rd button, like the Genius or the Mouse Systems drivers (Genius comes with a GTEST.COM utility, which you may use for testing).
* CuteMouse driver added a driver API extension to support the wheel; 3rd mouse button was already supported by earlier 3rd party drivers. Hardly any DOS software supports the wheel, just like the 3rd mouse button.
* VBADOS driver added an API extension allowing to check whether the emulator/virtualizer is using seamless mouse cursor integration; this extension is also supported at least by DOSBox-X, DOSBox Staging, and DOSEmu 2.
* VBADOS also added an experimental API extension (see https://git.javispedro.com/cgit/vbados.git/tr … c/wheelapi2.txt) to support support the 2nd (horizontal) wheel and additional buttons (4&5), but the driver with these updates wasn't released yet, plus I don't know about any software utilising these additions

Bonus:
* A bizarre device, Logitech CyberMouse 3D, also added an API extension to support additional axes, up to 7 buttons, and even a force feedback - but this is basically a separate API, described in the CyberMan 3D SWIFT Supplement document. At least Descent games support this device.