Sandy Bridge performance: what's it like?

15th Sep 2010 | 16:10

Sandy Bridge performance: what's it like?

Behind closed doors with an overclocked chip

Behind closed doors we came face to silicon with Sandy Bridge in its controversial overclocked state. But boy, did this one fly.

We got our sneak peek at this year's Intel Developer Forum (IDF) in San Francisco.

But speed isn't necessarily the real issue, and definitely isn't the reason for the controversy. No the controversy comes from the fact that with so much now integrated onto the CPU die - and subsequently plugged into the same clock generator, the baseclock - the heart-blood of the overclocked CPU, is now limited to around 100MHz.

This latest architecture from Intel then could signal the end of the road for the golden days of picking up bargainous chips and clocking the twangers out of them to, in essence, make your own £800 CPU analogue.

Previously we could take the likes of the Core i7 920, crank up the clocks, fool around with some voltages and ramp up the multipliers, then hit the same sort of performance you'd get from the absolute high-end of Intel CPUs.

With the Sandy Bridge chips though that is simply not going to be possible. The introduction of the enthusiast-facing K series chips this year, with their unlocked multipliers without the usual extreme price-tags, was a precursor to the only really overclockable Sandy Bridge chips.

Locked down multipliers

Sandy Bridge CPUs without the K moniker will have both practically locked down multipliers as well as that BCLK locked to 100MHz.

Dave Salazar, of the Performance Benchmarking and Analysis Group at Intel, was happy to talk about the locked clocks. "It is somewhat limited...it has to do with the fact that basically the ring-bus architecture, the cache, the CPU, all sit on the same clock domain. Bear in mind that the PCIe now sits inside the processor as well."

This means that when you try and up the baseclock of the CPU it affects a far greater number of parts reliant on that same clock generator. "While certain aspects of the part have greater tolerances to moving the baseclock," Salazar explains, "others parts do not."

The machine quietly humming away behind closed doors in the Advanced Technology Zone of IDF was one of the K series chips, and with a very healthy overclock indeed.

We are bound by NDAs, and by worries that large men in black suits will carry us away in the night. That means we can't reveal exactly what the speeds of this chip were, but running on air-cooling alone the overclocked Sandy Bridge CPU was running far quicker than the 4.2GHz you can usually squeeze out of the supposedly analogous current gen Core i7 875K.

This isn't a pre-production chip either.

Ahead of a 12 core Opteron

I couldn't get a final Cinebench R11.5 index score – the benchmark was running in an infinite loop to demonstrate the rock solid nature of this overclock – but Salazar was happy to say "it's north of that twelve core, twelve thread Opteron by a pretty healthy chunk".

And that AMD Opteron gets a Cinebench R11.5 score of 7.95, which compared to a Core i7 960's score of 5.48 makes the AMD server chip a pretty monstrous processing beast in its own right.

Salazar puts this healthy overclock down to the new relatively new production process as much as the new design, "that's the magic of 32nm making itself felt," he enthuses.

To be fair the overclock wasn't achieved just by virtue of the unlocked multiplier alone, there was a fair amount of voltage tweaking in evidence too.

"It is overvolted, Salazar says. "It's a pretty good overvolt, I'm not driving the hell out of it but it is overvolted."

So there's no worries then about the impressive overclocking prowess of the dedicated enthusiast K series of Sandy Bridge, but the non K monikered parts however will have a hard job keeping pace.

The future of Intel overclocking looks to be changed for good.

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