The second-generation Core processors arrived with a bang, but what sort of progress can you expect in the performance per watt department? We compare Core i5/i7-2x00 to AMD's Phenom with four and six cores, as well as previous-gen parts from Intel.

Intel’s next-generation desktop platform, code-named Sandy Bridge, has finally arrived. Our article, Intel’s Second-Gen Core CPUs: The Sandy Bridge Review, digs into the architecture and performance benchmarks of the new processors and chipsets, while the article you’re reading today focuses on power consumption and power efficiency.

Lower power consumption levels are no longer just nice to have, but in fact we’re observing that power consumption and power management are turning into features that ultimately also help maximizing performance in many popular load scenarios. This is even more important, as Intel designed Sandy Bridge to be modular, so that it can scale from entry-level Core i3 to the high-end Xeons later this year. Effectively, the majority of Intel’s mainstream processor portfolio will be based on Sandy bridge by the end of 2011, which makes an additional efficiency analysis worthwhile.

It was largely anticipated that Sandy Bridge would be capable of delivering more performance than Nehalem, and that it might use less power while delivering it. Our launch coverage already confirmed that Sandy Bridge (manifest in the Core i3-, i5-, and i7-2000-series), delivers substantially more performance than its predecessor. Architectural improvements are at the heart of this speed-up. An efficient ring bus, a decoded µop cache, improved branch prediction, larger buffers, widened floating point throughput, and improved memory availability all add up to notable clock-for-clock gains; we saw those all surface in the launch coverage, comparing Nehalem and Sandy Bridge in the single-threaded iTunes and Lame benchmarks.

In the end, Intel is moving more firepower and more features into existing segments. Although the LGA 1155 platform maintains the 95 W power envelope common in the company's mid-range portfolio today, Sandy Bridge processors are designed to radically shut off functional units when they aren’t needed. If you read our Sandy bridge launch article, you will probably remember that the processors feature a power control unit and three separate voltage and frequency domains. These facts are the main reason why LGA 1155 had to lose one pin (and backwards compatibility). The voltage regulators have to be capable of switching high currents much more responsively than before in order to properly support Sandy Bridge.

The S and T series bring thermal design power down to 65, 45, or even 35 W for low-power desktop applications by restricting clock speeds here and there. We will spend some time testing these offerings soon, but focus on the mainstream Core i5- and i7-2x00 series in this article.

Our efficiency testing is split into two parts. First, we look at systems with integrated graphics. Then, we compare machines with a discrete graphics card. The test systems with integrated graphics include an 890GX-based motherboard hosting AMD’s Phenom II X4 965 and X6 1100T. Picking slower AMD offerings would have moved the comparison price point too far down. We also added Intel’s H55 platform with the Core i5-661 and i3-530 dual-core CPUs, and H67 with Core i5-2500K and i7-2600K.

On the discrete graphics side, we grabbed the same AMD solutions, Intel’s Core i5-750 and Core i7-875K, and again the new Core i5-2500K and Core i7-2600K.