Does Turbo Boost Help Or Hurt Core i5/i7's Power Efficiency?

Power Play On TDP

Once upon a time, an Intel platform consisted of three components: a processor, a chipset northbridge (with a graphics interface and memory controller, also called the Memory Controller Hub or MCH), and a southbridge (the I/O Controller Hub, or ICH). The potential power consumption of these three components has to be added together. The processors are rated from 65W up to 130W, a P45 MCH requires up to 22W, and the ICH10R is rated at 4.5W.

The new LGA 1156 platform, including the Core i5-700- and i7-800-series CPUs, introduces Intel’s first mainstream two-chip design. The memory controller slipped into the processor with Bloomfield (Core i7 on LGA 1366) and the PCI Express interface now follows suit. As a result, the need for a separate northbridge is gone, leaving mainly I/O and management functionality behind. Given this slimmed-down arrangement, the P55 chipset is officially called the Platform Controller Hub, or PCH. Since large chunks of the PCH correspond to equivalent areas of the old ICH, net complexity and power consumption are similar.

Effectively, the new processors stay at the same power level as as some of the preceding Core 2 Quads: 95W. Compared to Core i7 on LGA 1366, the new processors are already rated 35W lower. Moreover, the fact that there's no longer a discrete MCH means that 20-some watt piece of logic no longer contributes to overall power consumption. Here is a summary:

The Math on Power Consumption

Core 2 Duo And P45
Core 2 Quad And P45
Core i7 And X58
Core i5/i7 And P55
Processor TDP65W
Northbridge TDP22W
Southbridge TDP4.5W
Total Platform TDP91.5W91.5 - 121.5W158.6W99.7W

If you look at the highest possible specified power levels, Core i7 and X58 top out at nearly 160W, while a Core 2 Quad platform requires up to 122W. The new processor’s sub-100W platform ceiling already represents a significant advance in potential efficiency without us having run a single power or performance benchmark. However, keep in mind that these numbers reflect maximum power consumption with regards to thermal limits (thermal design power). Reality might very well turn out to be a bit different.

The math also does not include power required by the motherboard and on-board components. Voltage regulators may be more or less efficient, and additional audio, network, or RAID chips all consume power, as well. We also have to add memory and a hard drive or SSD. Then there’s the graphics card. Entry-level models require around 20W idle power while high-end components easily eat up 60W and more without doing anything but displaying the Windows desktop. Hence we use a mainstream GeForce GTX 260² from Zotac, which is an efficient but still modern-enough model. Installing a faster graphics solution would just reduce the effective power consumption difference between various configurations based on Core 2 or Core i5/i7.