If you want to be organized, then the first thing you should know is you don't need to know where your main Poser runtime is, because you should not put anything in there.

You should be making external libraries (many of them) and install 3rd party content in those. Don't mix 3rd party stuff with your Poser stuff, for many many reasons. The least of which is you don't need to back up your main runtime because it installs that way and you didn't change it.

External runtimes (libraries) can and should be located where you want them and where you'll be able to find them quickly.

I make shortcuts in my explorer favorites for them and they're one click away.

 

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)