Kentsfield uses two dies in a single package and each die is a dual core unit, for a total of four cores on the processor. The reasoning behind using a two-die configuration is really one of engineering and money; its much easier (and thus cheaper) to glue two dies on a single processor package and thus the time to market is lower as well. Intel is able to beat AMD to the quad-core market because of this as AMD's designs are monolithic (single die). Another financial benefit is that having two dies allows Intel to bin their cores produced with a finer grain, putting faster cores on the more expensive processors, theoretically using two dies from different wafers on the same processor.



Link: PC Perspective