Hot Hardware have posted up a review of the Intel's Pentium 4 2.2GHz and 2.0GHz "Northwood" Processors. Heres a snip:
The all new Northwood Pentium 4 core now runs at a significantly lower power 1.5V core voltage. If there is one thing we would like you to take away from this article, it would be the concept of die geometry and how it affects processor power consumption, heat and speed. Intel's new .13 micron wafer fab technology allows for significantly smaller die size versus the older .18 process they are using on P4 "classic" Willamette core based devices. The smaller the die, the less power it consumes in addition to the inherently higher clock speeds that are able to be produced. Yields for this new P4 core have reached new heights in clock speed, now at 2.2GHz. for the top end processor.