The processor: optimized for longer battery life
It is important to remember that notebook processors and desktop processors are NOT the same. Notebooks have special mobile processors designed to combine high performance with maximum battery life. A mobile Pentium III processor consumes less than half the power of a comparable desktop processor.
Intel's processor range for notebooks comprises two lines: the Pentium III for high-performance machines and the Celeron processor for less demanding applications. From a technical point of view, there are only minor differences between the two types. The Celeron has slightly lower performance and a smaller cache, and is therefore offered at a lower price.

SpeedStep™ technology: cutting processor speeds to save energy
New technologies are being developed to enhance the control of power consumption of the battery. The logic of Pentium® SpeedStep™ technology is to offer the highest and stable clock speed when applications are running. When no application is running, the clock speed will reduce automatically. This technology allows low consumption of the battery. It also automatically detects whether the user is on AC adapter or on battery (dynamic frequency and voltage scaling) to deliver optimum balance between performance and battery life.