Performance or Power: Which Will Nehalem Use?

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Intel’s main obsession with the Core i7 processor, a.k.a. Nehalem, was power efficiency. If an idea wasn’t power efficient, the company said during Monday night’s launch event in San Francisco, it didn’t go into the chip no matter how good it was.

The change in the architecture has brought about what should be a considerable power savings, not so much from the CPU, but from other areas. For example, the elimination of the front side bus (FSB) and moving the memory controller onto the CPU will cut down on a lot of heat and power.

The FSB’s transistors go on and off hundreds of millions of times per second as data is routed between the CPU cores and memory. “That’s a tremendous power draw. Getting rid of that saves you a great deal of power, something AMD was able to do six years ago,” said Jon Peddie, president of Jon Peddie Associates.

The new Core i7 products, aimed at the performance desktop market, operates within the same thermal envelope as Intel’s existing Penryn-based products.

That, says Nathan Brookwood, research fellow with Insight 64, will allow for faster chips. “Power efficiency enables them to run at higher frequency and stay within the thermal envelope. What they are really saying is you get more performance for the same power envelope, as far as the processor is concerned,” he told InternetNews.com.

The other power argument is in the change in memory. Intel’s server products use Fully Buffered DIMM, or FBDIMM, which has a demonstrably higher power draw than DDR2 memory, used in desktops and laptops as well as Opteron servers, or the newer DDR3 memory.

More efficient servers coming

When Intel introduces Nehalem server products next year, those machines will use DDR3, which, combined with the new motherboards that are minus an FSB, should be more power efficient. How much more efficient is not clear, since Intel has yet to disclose server products.

The net of that memory change is there’s a savings from eliminating FBDIMM. “Having eliminated FBDIMMs is very helpful, especially on systems with lots of DIMMs. The rest of it is a wash, because they are taking advantage of whatever power saving they had with not having to power the FSB by running the chip at a higher speed,” said Brookwood.

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