Intel's QX6700

• Intel's first quad-core CPU was the Core 2 Extreme QX6700, released in November 2006. As you can see from the chart linked in Reference "QX6700 Power Consumption 1," this chip can be expected to draw well over 200 watts of power when doing heavy processing (encoding video, rendering three-dimensional objects, compressing files). Depending on what tests you use, this number can rise to almost 270 watts, as seen in Reference "QX6700 Power Consumption 2."
  
  

Evolving Requirements

• Improvements in power consumption were made down the line with the Q6600 and the Q6700, which managed to use about 10 percent less power. Intel eventually managed a solid balance between power consumption and performance, as seen in Resource "Q6600 and Q6700 compared to the rest." You can expect a current Core 2 Quad CPU to draw around 200 watts when under a full load (when you take into account that different hardware review web sites use different power consumption tests). To be on the safe side, make room for 250 watts when estimating what watt rating you want to have on your power supply.
  
  

The Computer as a Whole

• You might ask yourself why a person would want those 650-watt (or higher) power supplies that are so popular these days. After all, if a CPU is only using up to 250 watts, that should mean that a 650-watt PSU is overkill. And it's true that your storage devices and most components don't require hundreds of watts of electricity. However, there is one notable exception: the video card. While a quad-core processor might only need a roof of 250 watts, a quad core computer is a different story, as it usually contains a computer gaming-oriented video card.
  
  

Why a Powerful PSU Is Important

• Take a look at Resource "Video Card Power Consumption." Notice how these video cards use at least as much power as a quad-core CPU... when fully idle. When a modern video card is truly tested, it's not unusual for it to push the PSU past the 400-watt barrier. The system these video cards were tested on contained only one hard drive, no network card, no sound card, and no CD or DVD burners. Add in the usual components, and you can go well over 500 watts. In that case, you want to be using at least a 650W PSU for an average quad-core computer, and probably 750 watts, just to be safe.
  
  

A Word on AMD

• AMD, Intel's main competitor, falls somewhat in line with its Phenom X4 CPUs but tends to use about 10 percent more power on the high end of the product line. If you go with AMD, at least 750 watts would be prudent, if you have a computer gaming-oriented video card and multiple internal storage devices.