Lower Speeds Just By Halving The FSB Clock
Less than 100 MHz FSB clock (FSB400) is not possible on Intel's Socket 478 systems.
Halving the clock speed did the trick: At just 100 MHz FSB clock the Pentium 4 2.8 GHz in idle mode showed power needs of approx. 8.4 watts. Unfortunately, the power loss under load is still phenomenally high - our measurements with Prime95 showed 31.2 watts at 100% CPU load.
We pitted the 3.0 GHz sample of the P4 Northwood into the running with a x14 multiplier at 100 MHz FSB clock speed.
At a CPU speed of 1,400 MHz, the die temperature clearly cooled to as low as 34.5°C in an open system using the boxed cooler from Intel.
With the help of the ClockGen tool, the FSB can be switched down to 100 MHz during operation.
