LOL. You're unable to find this information? So I take it you never heard of Google?

In Google type "poser external runtimes"

First match:

Organizing Content: External Runtimes for Poser and DAZ/Studio
artzone.daz3d.com/wiki/doku.php/pub/tutorials/poser/poser-misc30

Third match:
Poser 101; Adding an External Runtime
http://covenantofcreativity.aimoo.com/Poser-Tutorials/Poser-101-Adding-an-External-Runtime-1-271538.html

Fourth match:
Tutorial: Setting up Multiple External Runtimes
http://www.posermocap.com/2008/09/16/tutorial-setting-up-multiple-external-runtimes/

I'll let you find the rest.

If you're specifically unclear on using external drives, yes it works. They can even be network drives, although these are usually annoyingly slow.

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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)