Does anybody have an article regarding the workings of I-VTEC. That's the system utilized by the K series engines too, right?

I realize it stands for "intelligent VTEC" but what I don't get is how it works or what makes it different. In my opinion VTEC is intelligent in and of itself as the engagement point is after a certain RPM, but can be even further depending on some sensors' readings including the TPS.

Can anybody give me an article or explain to me what makes I-VTEC....I-VTEC?