How does it actually work? Are there only two different positions, full boost and reduced boost? What PSI would a std RST make in each of these different positions?

And in which situations does the ECU switch over to reduced boost? I've heard that it happens somewhere up the rev range (5000 rpm?) to keep the engine safe.

Edit: Oh, and one more thing: What happens if I disconnect the plug from it? Will it stay on full or on reduced boost? I guess the latter, as I think full boost is opened by an electric impulse.