BigDaveX has it. The first gen P4 design was hot and didn't do so hot at typical server loads of the day. Intel needed something that provided improved performance on the lower end of the power envelope for mobile and high density servers. The Pentium-M and Pentium-S were their solutions. Both were based on the same core, with up to 512KB L2 cache that was running at die speed. They were specced out to 1.4Ghz I believe, with a 133Mhz FSB. If you did your homework, you could get the FSB up to 150Mhz and keep the core stable, which would get you most of the way to the memory throughput numbers for the quad pumped 100Mhz FSB of the early P4 chips. Coupled with the larger L2, they weren't really hamstrung by the slower memory bandwidth. On mobile, they gave much improved battery life, and thermals, for laptops as compared to P4-m, and only really struggled in certain FPU/SSE intensive situations. It turned out to be a smart move for them as it later evolved into Centrino/Core1/Core2.