Questions about kernel .ko and .so modules, rtapi-, hal- and more.

Hi,

Just a few questions.

If i search howto code and build a kernel module, all sites with examples use a .ko extension.
Normally i would compile linuxcnc with option "userspace mode" into .so extension.

All linuxcnc modules have then a .so extension and can not be loaded into the kernel that uses .ko modules.
Is it true that : rtapi_app is responible for creating a fictional realtime environment outside the golden ring?

My goal is to learn a bit more about the different types of kernel modules. And play around with it.