The Intel Core i7 860 Review

Last week Intel introduced its highly anticipated Lynnfield processors under the Core i5 and Core i7 brands. Three chips emerged:

We tested exclusively with the Core i7 870 and the Core i5 750, the 860 didn't arrive in my lab until after the review went live. I was spending the greater part of a week with AMD at that time and didn't get to testing until this past weekend. Here's the chip:

What makes the Core i7 860 so interesting is that it's priced on par with everybody's favorite Nehalem: the Core i7 920. The 870 has great turbo modes, but it's nearly twice the price of the 860. The Core i5 750 wins in the price department, but it lacks Hyper Threading - part of what makes Nehalem so tasty in the first place. The 860 effectively gives us the best of both worlds, hence the focus on it for today's review.

I had a few mistakes in my original version of this table, but below you can see the turbo modes offered by the 860. They're not quite as nice as the 870, but the chip is also half as expensive. You'll also see that like the 750 you only get a single bin improvement with 3 or 4 cores active, but like the 870 you get 4 and 5 extra speed bins in the dual and single active core situations:

I've explained turbo mode in great detail here. In short, Lynnfield's PCU (Power Control Unit) looks at the number of cores active, shuts down those that are inactive, and uses the thermal savings to boost the clock speed of the active cores - all within the operating specs of the processor. Unless you're overclocking, turbo will never compromise system stability in search of greater performance.

It works very well in practice, particularly with Windows 7. A question that's come up since the initial review is what happens when background tasks kick in. As I mentioned in the "Speed Limits" section of the Lynnfield review, this is something that can prevent turbo from kicking in:

"There's also the issue of background threads running in the OS. Although your foreground app may only use a single thread, there are usually dozens (if not hundreds) of active threads on your system at any time. Just a few of those being scheduled on sleeping cores will wake them up and limit your max turbo frequency (Windows 7 is allegedly better at not doing this)."

One of the features of Windows 7 is that the OS supposedly does a better job of grouping tasks together on a single core to avoid waking up an adjacent core and negating the gains from turbo mode. I'm still working on finding a good way to measure this but from what I've seen initially, Windows 7 tends to do a good job of grouping threads onto one or two cores - meaning we tend to see the 4-bin or 5-bin turbo modes. The other thing to keep in mind is that the processor can turbo up/down faster than the OS can schedule threads, the benefits of turbo are present even while in the middle of executing a task. Remember what dictates turbo is both thermal dissipation and current consumption; the mix of instructions executed varies depending on the task and even during the task, which in turn varies the frequency your core(s) will run at.

The end result is a system that seems to feel more responsive as well as perform better. Of course none of this matters if you're going to be disabling turbo and just overclocking, but I've addressed that scenario in a separate article today :)

And I don't really have a reason for showing this, but I like tables so here's the current quad-core processor landscape:

The Test

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