I posted about this a few months ago, but have a different set of questions about this now.

I have a P5 MB with an integrated controller that supports 2 drives, but want to add a 3rd floppy drive. So I built Sergey's Monster Floppy controller and populated only the secondary controller, which is on 0x370.

The add-in card controller works if I use a DOS driver like DOSFDRV.SYS and no floppy BIOS. But once I enable the onboard floppy BIOS, things just act weird. It won't boot from the integrated controller, won't boot from the secondary controller, and occasionally freezes during BIOS when announcing the presence of the floppy BIOS (might depend on the floppy BIOS settings). And I can't access any floppy drive in DOS.

Now, the floppy BIOS does appear to support two controllers with no way to disable the first, other than not installing the jumper for 0x3F0. But I wonder if the BIOS is clashing with the onboard. However, even if I disable the onboard floppy controller, it still won't boot from the add-in controller.

I don't understand what occurs during boot with regard to floppies. Is what I'm trying to do simply fraught with issues? Am I better off forgetting about the BIOS and just be happy that the driver operates the secondary controller? I think it would be nice to not have to use the driver, but maybe I can't do that.