... Under Heavy CPU And Graphics Load
Adding a heavy load on the GeForce 6800 GT (for which we used the PowerVR benchmark) raised the systems' power consumption by almost 50 Watts.
... When Idle
For our tests during idle operation - i.e., Windows running, but with no application active - we enabled AMD's Cool & Quiet and Intel's SpeedStep whenever possible, to achieve the lowest possible thermal loss. The Pentium M continues to be the most energy efficient processor, no matter at what speed it operates. Close on its heels is the Pentium 4 Northwood between 2.8 and 3.4 GHz, running on the same platform.
These results are influenced by two somewhat opposing factors. On the one hand, the 130 nm Pentium 4 is not as strongly affected by the problem of leakage currents. On the other hand, the i865/875 platform is more frugal than the i915/925 chipsets, whose components are often equipped with cooling solutions by all manufacturers.
The Pentium 4 models of the 600 series seem to benefit quite a bit from the inclusion of SpeedStep. The automatic reduction in clock speed from 3.4 GHz to 2.8 GHz reduces the power draw by 30 W. The savings on the Athlon 64 are not as pronounced, as the core has a lower thermal loss to begin with.