I agree, it is worth upgrading to P5 to be able to use external runtimes. Not only can you use external runtimes on other drives of the same computer but also on drives of a networked computer providing, of course both computers are running. I recently bought a new computer to which I transferred P5 but I still use runtimes on both d: and c: drives of the old computer whilst installing new items into runtimes created on the new computer. The only items I have had to install on the new computer are Daz ones. They seem to have difficulty finding the geometries of some items.