2. Powernow = The Power You Need, Consistency + Least Possible Energy Use

Grossly oversimplified, that's the formula that best describes the mobile Athlon XP's power management. What is behind the development of PowerNow! is a very simple idea: working on a mobile PC system does not constantly require maximum processing power. This makes it legitimate to reduce the clock rate and the input power during times when the processor is not working at full capacity. That not only helps to save electricity and increase battery life, but also causes less heat to be generated when the processor is running at a low ebb, allowing for a notebook design that, acoustically speaking, keeps a low profile. If more computing power is needed, the voltage and clock rate of the processor increase automatically. If power requirements drop again, both rates decrease, bringing down the power uptake of the processor.

Unless pre-set in the power scheme by the user (see below), this behavior is controlled completely automatically, without making it necessary for a user to make changes to the operating system and BIOS. All the while, the operating system continuously measures the processor load and communicates with the processor, via a driver, in order to set the correct clock rate and voltage dynamically. The possible clock rate-voltage combinations are stored in the power scheme in the notebook's BIOS and cannot be altered by the user. Depending on the processor, different clock rate-voltage combinations are possible. When programming the power scheme, the developer also determines whether all possible clock rate-voltage combinations or only a portion of those possible are used.

This is where AMD's PowerNow! distinguishes itself from its counterpart, Enhanced Speedstep, which Intel uses in both its Mobile P3-m and its Mobile P4-m; Enhanced Speedstep currently offers two clock rate-voltage pairs to control the energy use of the processor.

The mobile Athlon XP 1800+ used in the Compaq Evo N1015v is controlled with a 266MHz FSB. The maximum clock multiplier is 11.5, while the minimum is 4. In the test, the following multipliers and corresponding processor clock rates could also be identified.

The voltages used with the respective multipliers are, on the other hand, not transparent for the user.