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Power Consumption

Intel’s Mobile Core i5 And Core i3: Arrandale Is For The Rest Of Us
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The Core i5-540M is a 35W processor, whereas Intel’s Core 2 Duo P8700 is a 25W part. Thus, it’s hardly a surprise to see the Montevina platform using less power in Prime95 than the newer Calpella design (note that these numbers were taken with no battery installed).

In fact, we certainly expected Arrandale to use more power under load based on our previous experiences with Core i7-920XM. In that story, we saw Turbo Boost and Hyper-Threading maximizing performance, depending on workload, at the expense of power consumption, whereas Core 2 Quad (or Duo, in this case) is unable to deliver a dynamic performance story.

The match-up gets much closer at idle. Although the i5-540M sports a higher TDP and two-die package, it also employs a two-chip platform and power gating to minimize the consumption of unused resources.

However, these min./max. figures don’t tell the whole story, so we also recorded a PCMark Vantage run on each notebook and charted out power use at two second intervals.

Although the 35W Core i5-540M clearly uses more power under load, it also dips well under the Core 2 Duo P8700 during Vantage’s down-time, despite the load/idle numbers above.

When you even out all of the peaks and valleys, you get 32.9W average power consumption for the Arrandale processor and 31.7W for the Penryn-based Core 2 Duo. When we factor in the fact that the Core i5-540M system finished the test 2:26 faster than the Core 2 Duo, dropping back to idle as the other machine completed its workload, we’re able to conclude that there’s finally evidence of Nehalem-based processors outdoing Core 2 when it comes to overall power consumption. The performance story tells itself. Arrandale is clearly the quicker chip, too.

This is something we’ve been waiting on for a while now. First, we heard about power gating, which would shut down unused processing cores almost completely. Then there was the inclusion of PCI Express and memory control with Lynnfield. Adding Windows 7 to the mix was supposed to optimize power usage further. But each step along the way, we saw the Nehalem design using more power than we had expected. “Wait for Arrandale, wait for Arrandale, wait for Arrandale,” was what we kept hearing. Now that Arrandale is upon us, we see the wait was worthwhile. The two-chip platform architecture, heavy integration, and shift to 32nm manufacturing means it’s now possible to get significantly better performance from a dual-core, four-thread CPU at lower overall power use than a comparably-equipped dual-core notebook based on Core 2.

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