I am trying to understand what kind of harware device the Plus module is. I see a small (very small) port on the back. Is this where it "plugs in"? Also, does the Plus module replace the existing ti-92 CPU? Can you remove the Plus module and replug it switching between the two processors? I seem to be getting the idea it is more like a co-processor rather than say a 486 replacing a 386. I have read the faq and am not sure .....