Intel Core i7 875K £310

20th Jul 2010 | 11:40

Intel Core i7 875K

Intel brings unlocked overclocking larks to mainstream CPUs

TechRadar rating:

4 stars

Quad-core K series a welcome addition. Pity it's not affordable. Bring on the 755K, please.

Like:

Lots of overclocking options; Awesome performance; Cheaper than an 870

Dislike:

No extra OC headroom

Intel Core i7 875K - Overview

If you want a Core i7 chip for overclocking the unlocked Extreme Edition chips were the best around, but the K-series from Intel, like the Core i7 875K CPU we've got here, could well fill the gap.

The Extreme Edition processors from Intel always have been and always will be overpriced irrelevancies. What else can you say about a series that typically cost upwards of £800?

The problem isn't just pricing, either. In outright performance terms, Extreme Edition chips are often no more than 15 to 20 per cent faster than CPUs costing a third or less the price. Value for money they most certainly ain't.

Of course, the latest Extreme is a bit special thanks to offering more cores than any other Intel processor. But with more mainstream six-core chips pencilled in for later this year, even the Core i7-980X will soon resume the Extreme Edition's traditional rip-off role.

Despite all this harshing on Intel's flagship CPU line, however, there's one aspect of the Extreme family we've always loved: the unlocked CPU multiplier. It's a feature that makes for idiot-proof overclocking and takes memory out of the equation.

It's also a feature that would be trivial for Intel to add to any of its current CPUs. Wouldn't it be nice if you could have the unlocked multiplier in a more affordable chip? In fact, you already can if you go for one of AMD's competitively priced Black Series CPUs.

And perhaps it's the AMD Black chips that explain the arrival of Intel's new special K pairing. Yup, Intel has released a couple of cut-price processors with unlocked multipliers that are aimed squarely at performance enthusiasts.

Say hello, therefore, to the new Core i7-875K. The new K-series chips are closely related to existing processors in Intel's desktop range. The 875K lines up next to the Core i7-870.

The base clockspeed is 2.93GHz with a top Turbo of 3.6GHz, theoretically anyway. In our experience, you won't always see a full return on that Turbo promise.

Anyhoo, the 875K is a Lynnfield processor and thus a quad-core 45nm specimen with two threads per core, a dual-channel memory controller, 8MB of L3 cache and a 95 Watt TDP. Again, all of the above is shared with the plain old 870.

Beyond those headline specs, there's not all that much to know. The K-series chips drop into the LGA 1,156 socket and come boxed and branded with a big silver flash reading "Unlocked". More significantly, they also come sans CPU cooler. That's not a huge vote of confidence in Intel's stock heat sinks. Nevertheless, it's the right call. Most overclocking enthusiasts would prefer to choose their own cooler.

More intriguing is that Intel has positioned the 875K £100 below the 870.

That's right, the 875K has identical clockspeeds and cache, adds the unlocked multiplier but will typically sell for £310 to the 870's £420. Admittedly, we always felt the 870 was seriously overpriced. Yet this topsy-turvy positioning from Intel seems completely bonkers. But then, Intel's marketing is madness all round at the moment.

How else can you explain the fact that Intel introduced a new branding scheme in the Core i3, i5 and i7 monikers that was supposed to add clarity but only confuses. There's no way of telling from those brands how many cores you're getting or even which socket a CPU drops into.

Intel Core i7 857K - Benchmarks

Overclocking is what the K series is all about and that's precisely what we focused on.

Given the enthusiast remit, we upped the voltages along with the core clock in order to squeeze the max from Intel's new special Ks. The brutal truth is that the Core i5 655K is simply too pricey for a dual-core chip.

It's therefore the 875K that really grabs our attention.

It's worth noting that it uses more power at stock frequency settings. That reflects the fact that the 875K isn't a special new stepping. It's the same (slightly) old Lynnfield core but with an unlocked multiplier.

HD Video Encoding performance

Intel k-series benchmarks

3D Rendering performance

Intel k-series benchmarks

Memory Bandwidth

Intel k-series benchmarks

CPU Gaming Performance

Intel k-series benchmarks

Intel Core i7 875K - Verdict

Intel core i7 875k main

Out of the box, the 870 and 875K are unsurprisingly very close when running at default settings. Slightly disconcertingly, it's actually our dusty old 870 that has the slight edge.

The fact, for instance, that it's one frame per second faster in the X264 HD video encoding test isn't much of a worry. It's close enough to be statistically insignificant. But the 870's five Watt power consumption advantage, both under load and at idle, doesn't bode well. Chips that clock up well also tend to be chips that use less power.

Time, then, to unleash those clocks. With the 875K, you have plenty of options. Like any Lynnfield chip, you can give the baseclock, set to 133MHz as standard, a twiddle. The problem with that, of course, is that you'll take the memory clocks with you. You'll definitely end up with your memory running at some funky non-standard frequency and at some point you will have to step in and knock the dividers down a notch or two.

Much better, therefore, to avail yourself of the 875K's unlocked multipliers. Here you essentially have two options. You can either go old school, switch off the Turbo function and ramp up the global multiplier setting for all cores. With the 875K, the multiplier range extends from nine to 63. The latter works out at 8.4GHz, so let's just say you have plenty of scope. The other option is to bring Turbo mode into the equation.

Not only can you adjust the Turbo settings per core. In other words, you define how many steps Turbo increases the multiplier when anywhere from one to four cores are under load. You can also fettle the wattage and amperage cut-off points for Turbo mode, theoretically giving the chip more headroom.

But to cut a long story short, ditching Turbo and going global tends to give the better results. Even with the Turbo wattage and amperage ceilings raised, the 875K won't run consistently at overclocked Turbo speeds.

Unfortunately, what it also won't do is run any faster than the old 870. Both chips top out at 4GHz with the CPU voltage upped to around 1.35V to 1.375V, the latter being a range we're comfortable with regards long-term reliability. Unsurprisingly, there's little to choose between the two in our overclocked benchmark results.

Given that the 875K is much cheaper than the 870, the new K series offering is still a no-brainer. But it's still disappointing to find the unlocked multiplier doesn't translate into at least a little more oomph.

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