If the goal is building an energy efficient system, choosing the right components is imperative.

As our measurements impressively demonstrate, choosing a 3-phase power design over a 6-phase design can mean a difference of 6 watts when the system is idle. In other words, buying a low-power CPU will not automatically make for an energy-efficient system. Instead, other components such as the motherboard and the power supply need to be selected carefully as well.

3-phase voltage regulator on the ECS board

Foxconn's board uses a 4-phase design.

In the notebook arena, Centrino systems have had the ability to shut off individual phases of the voltage regulator when they are not needed for quite a while. Hopefully, this technology will make it to the desktop space in the near future.

We can see at a glance that AMD's processors are as yet unbeaten when it comes to low idle power consumption. However, Intel can finally begin to close this gap with its L2 stepping, although this is still not quite enough to trump AMD's offerings. Therefore, AMD's processors retain the crown for lowest power consumption when idle, aided by the fact that chipsets for the AMD platform also tend to have lower power requirements. One of the reasons for the greater power demands of the Intel processors is their comparatively high clock speed when idle. While AMD's processors underclock themselves all the way to 1 GHz, Intel's Core 2 CPUs still run at 1.6 GHz, thanks to its higher multiplier. Why Intel didn't remedy this situation with the introduction of the Conroe design remains a mystery to us. In the notebook space, Intel uses an identical core with the ability to slow itself down to 1 GHz due to its lower FSB of 166 MHz. In theory, the Conroe core should therefore be able to run at such low frequencies without any trouble.

Under full load, the picture changes, and we can see that Intel has been able to improve its processors' efficiency over the last few years. AMD, on the other hand, has lost ground in this discipline, due to the fact that it is still using the same architecture. With regard to power dissipation, the Core 2 Duo E6300 using the L2 stepping is able to challenge AMD's EE CPU. However, raw performance is what ultimately matters under full load. In other words, we'll have to factor in the processors' individual performance into our rankings as well. We'll cover this aspect in more detail later, when we look at the efficiency measurements.