Spire's Gemini SP986B1-V2-2P heatsink is a minor variation on the popular Eclipse II tower heatsink design, the most notable difference being a novel bifurcated fin stack. To 'bifurcate' means to split into two... so in other words, the fin stack is split down the middle and the fin edges are closed off so air can only pass through the heatsink from front-to-back. This unique 'ducting' approach essentially creates two independent fin towers connected by six, 6mm diameter U-shaped sintered metal wick copper heatpipes. As the center part of a heatsink typically receives the least amount of airflow, this approach aims to direct a higher volume of air through the section of cooling fin which receives the most heat from the heatpipes.
FULL STORY @ FROSTYTECH (http://www.frostytech.com/articleview.cfm?articleID=2606)