Mobile CPUs sometimes lead technology, with the 100 MHz front side bus of mobile Celeron processors or with the introduction of new manufacturing processes like the .18um process and the on-die level two cache starting with Pentium II.
Mobile CPUs follow technology with the front side bus of 100MHz with mobile Pentium III processors or the late introduction of Pentium III to the mobile market.
Notebooks are complete PCs with a weight less then 4kg.
You can have a desktop replacement with a 850MHz Pentium III or a thin and light notebook weighing less then 2kg and a low voltage 500MHz Pentium III.
Within certain limits you can upgrade the CPU of your notebook. But you will not be able to upgrade the notebook motherboard if you want to support a complete new range of CPUs.
Every board inside of a notebook is custom made for that notebook model. Upgrading a Pentium II with TDPmax 11.5W to a Pentium III with TDPmax 27.5W requires much more then just a motherboard change.
There are only very few standards for a notebook design. The notebook motherboards are being designed around the devices like battery, HDD, FDD and DVD/CD-ROM. Every bit of space is being used to squeeze in the chips and to provide the best thermal support.
But all of this will be material for several follow-up articles. So, stay tuned for the new section of tom's hardware guide - the mobile guide.