Registering for college classes?

Hello, I attend an undisclosed university and I just had one simple question that was kind of confusing me. You must bare with me I am only a freshman. However, I was wondering that why my school requires us to register for fall 2011 classes so early? We register for them March 15th and fall semester starts August 31st. I will be a sophomore in the fall 2011 semester by the way. Just curious, as I am lost in this registration process.