Airbus A380 engine question

I don't know enough (make that anything) about aircraft engines, here are their sites.

Rolls.

http://www.rolls-royce.com/civil_aerospace/downloads/airlines.jsp

P&W

http://www.pratt-whitney.com/prod_commercial.asp

The General Electric and Pratt & Whitney engines are twin spool setups, one spool for high speed turbine and compressers; the core, the other spool is the low speed turbine and the bypass fan which of course makes the bulk of the thrust. The Roll Royce Trent's are triple spool setups. I'm not sure what the third spool does. I suspect the extra spool is involved with making the engine core a little more efficient in it's fuel burn. I have read that the third spool's benefit is problematic versus the maintainance and reliability difficulties associated with the Trents. The extra efficiency barely outweighs the extra costs of maintainance. There has been some work done by GE using a geared spool for the low speed turbine and fan. The setup uses a centerless planetary gear reduction unit between the turbine and fan. By speeding up the turbine and actually slowing down the fan, the engine produces about 8% more thrust and is 9-11% more efficient than conventional twin spool designs. One other difference between the GEs, Pratts, and the Trents is the thrust reversers. The Trents use doors just behind the fans not unlike the old buckets used on the old strait pipe jets like you see on the older 737's.

Thanks both for the replies.
I find this stuff very fascinating, always have.

Dave