Intel Core i7-2600K review

After months of speculation and rumour, Intel’s Sandy Bridge processors are finally with us. In fact we’ve been testing them since mid-december, but Intel’s strict non-disclosure agreements have silenced us till this morning. Now, though, that Sandy Bridge codename can be thrown off to reveal Intel’s true naming strategy of … 2nd Generation Core i7, i5 and i3.

Hardly thrilling is it. The new processors are hugely improved over the old models, as we’ll explain, with serious architectural changes and a whole new socket and chipset to support them. Despite this, Intel has insisted in keeping the same basic branding, only with the processor model numbers extended to four digits.

Worse still, it now means there are no less than three different processor sockets under the Core i7 brand: LGA1366, LGA1156 and the new LGA1155. Yes, that’s right, the new Core processors require a new socket – meaning you can’t upgrade your current PC. The LGA1155 socket will appear on motherboards with the new P67 and H67 chipsets – see our reviews opposite for more details on the capabilities and limitations of these new chipsets.

Thankfully, Intel can be partly forgiven for all this, as it has produced a corker of a new architecture. This release represents the Tick of Intel’s Tick-Tock strategy. This means that it retains Nehalem’s 32nm production method, but has a revised architecture.

The most obvious feature of the new design is that all the new processors have built-in graphics chips (unlike the mix and match selection of the last generation). These are actually integrated into the processor die too, rather than as a separate piece of silicon sitting alongside the processor in the same package. This may seem like a technicality, but it allows the two to share the processor’s L3 cache, and to balance their power needs and heat output as one – both can be dynamically clocked according to your needs.

The graphics hardware has other improvements too. With HDMI 1.4a for stereoscopic 3D Blu-ray playback at 1080p, and output of HD audio bitstreams such as Dolby TrueHD, those with Media Centre PCs will no longer need a low-end graphics card to satisfy their video and audio output needs. We saw stutter-free playback of Blu-ray quality video with almost no processor overhead.

Gaming performance has also improved, though card manufacturers still don’t have a lot to worry about here. The HD 3000 graphics in our Core i7-2600K run at up to 1,350MHz, which sounds very high compared to core speeds on modern graphics cards. Despite this, it only managed a playable 27.2fps in our Call of Duty 4 test once the resolution had been reduced to 1,024×768 and anti-aliasing was disabled. At our usual settings, it produced just 6.0fps. However, it’s a big step forward to say that many games from only a couple of years back will run acceptably on this built-in chip.

The greater processing power of this chip can also be used to accelerate intensive tasks, such as video encoding; with support for hardware encoding of MPEG2, VC1 and AVC video streams up to 1080p. Unfortunately, we haven’t yet had a chance to test this with consumer software, but we will be covering it in upcoming media suite reviews.

Turbo Boost has been improved as well, with version 2.0 – though most of the modifications are more applicable to the upcoming mobile versions of the chip. For example, it can borrow power budget from the graphics segment when that’s not in full use, and even boost beyond the heat-dissipation capabilities of the attached heat sink for short periods of time. Mobile chips will even be able to draw power simultaneously from mains and battery if they require extra wattage.

Looking at the Core i7-2600K in more detail, and its locked sibling the i7-2600, we can see that it benefits from Intel’s HyperThreading Technology. This means that each core is seen by the operating system as two cores, and so two instructions can be prepared for it simultaneously, improving efficiency. It has a massive 8MB of shared L3 cache, so there’s no bottleneck getting instructions to the cores.

Intel lists its base frequency at 3.4GHz, though this is largely meaningless as the multiplier is forever flicking up and down depending on the task at hand. At stock speeds it Turbo Boosts up to 3.8GHz. Even using these settings we saw incredible results from the i7-2600K. It scored 183 in our single-threaded image-editing test, an incredible 204 in our video encoding test and 162 in our multi-tasking test. This amounted to an overall score of 186, actually faster than Intel’s £800, six-core monster – the i7-980X. It’s an incredible result from such a small and power efficient piece of silicon.

With Turbo Boost, we initially thought Intel was trying to bring overclocking out of its murky hobbyist niche. However, with Sandy Bridge it’s gone well beyond that, with affordable and easy to overclock processors. Previously, the only Intel processors with an unlocked multiplier were incredibly expensive Extreme Edition chips. Now, both Core i7 and Core i5 ranges have a K-designated processor with a fully unlocked multiplier. These cost a few pounds more than the regular versions, which you could view as a rip off, as Intel are charging you simply to disable their own security. Then again a lot a of time and research has gone into making these chips run fast and cool, and it’s overclocking enthusiasts who will benefit the most from that effort.

The new processors have a low base clock speed of just 100MHz. This means you can make fairly fine speed adjustments by adjusting the multiplier setting. Overclocking primarily via the multiplier is an essential change, as pushing up the base clock speed throws out other devices and data buses associated with the processor. To overclock the processor, you simply raise the maximum multiplier ratio in the BIOS. Even the locked versions of the chips can have their multipliers raised by up to four steps, equivalent to 400MHz, while the K-designated chips are theoretically unlimited.

We pushed up the multiplier by four steps on our Core i7 chip, to a maximum clock speed of 4.2GHz. We had no stability problems and saw the overall score shoot up, as it ploughed through our benchmarks at high speed. Once overclocked in this way, we noted that Turbo Boost became far more aggressive than normal, maintaining the top speed almost constantly. This produced an incredible overall score of 214, and this from just a minor overclock available on even the locked version of the processor.

These overclocks raise the maximum target speed, so the processor will throttle back if it overheats. However, by using a large tower heat sink with three heatpipes, we saw the chip maintain 4.2GHz throughout even our multi-threaded video encoding test. Don’t expect to see this consistent performance using the smaller stock heat sink.

Better still, Intel’s SpeedStep still functions when the processor is overlocked, so it drops back down to a x16 multiplier when it’s idling – keeping things quiet, cool and power-friendly. The processors are incredibly power efficient anyway, with a TDP of just 95W, and that covers CPU and graphics, remember.

Much of the thinking behind the new architecture has been informed by designing a mobile processor. That includes the built-in graphics, clever power management and a small physical package. However, none of these are unwelcome in a desktop PC either, and with benchmark results like these, it’s impossible to complain about the result.

The Core i7-2600K is an incredible processor, and a worthy winner of our Ultimate award. However, unless money is no object, you shouldn’t buy one. That’s because the Core i5-2500K is available for around £80 less, that’s almost the price of a compatible motherboard, and yet retains the vast majority of this chips performance.