Performance or Power: Which Will Nehalem Use?

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

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.

Next page: No good watt goes unused

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No good watt goes unused

Intel is off to a good start with a 3.2GHz Core i7. The top of the line for desktop quad cores is the QX9775, and it maxes out at 3.2GHz as well, which means Intel could come out with a faster i7 thanks to its Turbo Boost technology.

Turbo Boost turns off cores that are not in use with a new technology, called power gate, that turns off all power to the core. That’s not just putting them in idle or standby mode, that’s shutting them off completely. Power can then be routed to the core or cores in use to give them a minor power bump if they are being particularly taxed.

That bump might be about five percent or less, depending on the speed of the processor. The 2.66Ghz Core i7 would get a bigger bump than the 3.2GHz i7 would, since the 2.66Ghz chip is running slower to begin with.

What remains to be seen is the impact this will have on servers. Nehalem servers will have a new CPU, one less power-drawing chip on the motherboard and memory that draws a lot less power. That could mean lower-power, cooler servers in the future, something that would be welcomed in datacenters, where power and cooling is a major concern.

“This is disruptive technology in a good way,” said Rob Crooke, general manager of the Business Client Group at Intel during a question and answer session at the launch event. “Our goal was to require the same amount of power to get higher performance. The thermal designed footprint for this is held constant or reduced so you can get more computing out of the same footprint or less.”

Peddie doesn’t think it will change much, however. “I think the simplest model is [datacenters] will use their air conditioners less than they used to, which will save them some power, and their power bill will be less than it used to be,” he told “I see it as a benefit and a bonus but I don’t see them doing anything dramatic with it.”

However, Brookwood thinks power savings will just be used up elsewhere. “People will take more power if they can get it. They are taking advantage of whatever power savings they had by not having to drive that humongous front side bus to run the chips at a higher temperature or a higher speed,” he said.

Intel plans to discuss its Nehalem server plans next month.

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