AthlonXP Underclocking for a Low-Power Fix

As A Point Of Comparison: Intel Pentium 4

The Asus P4P800's BIOS offers all the technical means to raise or lower the FSB clock speed.

The slowest Pentium 4 still available is the 2.8 GHz model for Socket 478 based on the Northwood core. Given that the current models work at 200 MHz FSB (FSB800, quad-pumped), these processors also offer the potential to halve clock speed by reducing the system clock to 100 MHz (FSB400). Values below this are not possible, however, since Intel does not release its CPU's multipliers - any number of tools or smart BIOS developers won't change this.

Almost all motherboards offer the opportunity to adjust the FSB clock speed in the BIOS, including Intel's own models. If your BIOS does not support this, you can still fall back on utilities that address the clock generator directly (see above, ClockGen). Less than 100 MHz FSB is not possible, however, which limits the P4 2.8 GHz P4's lowest possible speed to 1.4 GHz. A model with 2.4 GHz and FSB800 can thus be underclocked to 1.2 GHz (multiplier x12).

Due to the binary codes for the core voltage hardwired into the Pentium 4, the motherboard adapts itself automatically to these voltage settings. This means many motherboards do not allow a lower voltage than this, dashing hopes of further cuts in power losses.

What's happening at Intel?

Whoever thought that the P4 Prescott would represent the peak of power consumption ought to know better after taking a look at the Prescott in the Socket 775. The new generation gobbles up even more power.

To counter this questionable development, the next stepping (a development stage in a complex chip) under the codename E0 offers a range of additional features. Thermal Monitoring 2 is thus able to vary the core speed on the fly, according to CPU load, similar to mobile processors, in order to lower average power losses. It's understandable that Intel avoids comparisons with SpeedStep, and thus designates the new function simply as "demand-based switching."

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