Power Consumption

The reduced platform power consumption of the Core i5 and Core i7 CPUs is immediately apparent, even at idle. Both Lynnfield-based designs dip in around 20W underneath the Core 2 Quad Q9550S, which we’ve been using up until this point to replicate the performance of a standard Q9550. The ‘S’ model has a 65W TDP though, so the fact that Core i7-870 and Core i5-750 suck up less juice at idle is impressive. So too is the idle consumption of AMD’s Phenom II X4 965 BE, which also ducks in under the Core 2 Quad.

Fire up the Small FFT test in Prime95, add a FurMark Burn-In test, and the power usage jumps through the roof. Here’s where Intel’s low-power Q9550S shines, turning in the best results. But the two Lynnfields continue to impress with the second and third lowest power consumption figures. AMD’s Phenom II X4 965 comes in fourth, followed by the Core 2 Extreme, and trailed by the 130W Bloomfield-based Core i7-920.

It can be difficult to take thermal design power specs and give them real-world meaning. However, when you do the math, these load numbers make good sense. The TDP of Intel’s low-power Core 2 Quad is 30W below Lynnfield’s spec. Subtract out a power-hungry northbridge and you’re looking at the gap we see here in practice. Add 22W to the X58’s power budget and then take Bloomfield’s 130W ceiling into account; it’s no wonder Core i7-920 sits at the other end of the spectrum.