Intel Core 2 Extreme QX6850

Verdict: Four cores + 1,333MHz FSB = breathtaking performance

Although the Extreme Edition series got off to a wobbly start in the NetBurst Pentium days – it was much more expensive than standard CPUs, but not much faster – the brand took a turn for the better when Intel started using the Core architecture. The first such chip was the Core 2 Extreme X6800, which was soon followed by the first quad-core CPU, the QX6700, and then by a slighter higher clocked model in the form of the QX6800. It should come as no surprise, therefore, that as well as the new 1,333MHz Core 2 Duos, there’s also a new Extreme model: the Core 2 Extreme QX6850. Sensibly, this quad-core CPU still comprises two separate dual-core dies packaged together.

This makes manufacturing quad-core CPUs much easier and more flexible than the single-die approach of AMD; Intel can simply cherry-pick dies from dual-core production lines, making quad-core parts as demand dictates. With this simple and sensible approach to quad-core production, Intel is already selling its tenth quad-core CPU, while AMD has yet to make its first.

One downside is that Intel has to match the two dual-core dies, since the LGA775 socket only provides one voltage plane. Even so, here’s some leeway, since cores 0 and 1 ran 3-5 degrees C hotter than cores 2 and 3 in our test CPU. Another downside is that the 8MB of Level 2 cache is split across the two dies, with each pair of cores sharing 4MB. Each core retains 32KB of Level 1 cache.

The QX6850 has the same hefty 130W TDP as that of the QX6700 and QX6800, so it requires effective cooling. However, like all Core 2 Extremes, the QX6850 is very hardy; it’s happy up to 100 degrees C, while a standard Core 2 Duo will throttle its speed at 85 degrees C. Not only is the QX6850 armed with a faster FSB than the QX6800, which had an FSB of 266MHz (1,066MHz effective), but it also runs faster at 3GHz, rather than 2.93GHz. This may only be a 67MHz increase but, combined with the higher FSB (which provides the QX6850 with more memory bandwidth than the QX6800), the QX6850 should be faster.Like all Extreme CPUs, the QX6850 has an unlocked multiplier, so it’s easy to overclock.

To find out how much of a difference these higher frequencies make, we tested the QX6800 and QX6850 in the same test rig. This was the same PC that we used for the CPUs on the opposite page, so you can directly compare all the results on these two pages. While the dual-core 1,333MHz CPUs were no faster than their 1,066MHz counterparts, this chip proved to be faster than its predecessor, and by more than the extra the clock speed merits. The QX6850 was a good 6 per cent faster than the QX6800 in the memory bandwidth intensive multitasking test (making it 0.14 faster in our scoring system). Comparing only frequencies, this QX6850 is just 2 per cent faster than the QX6800; clearly, the increased FSB does a better job of feeding the four cores.

Following this discovery, we eschewed the usual approach of overclocking a Core 2 Extreme by increasing its bus multiplier in favour of increasing the FSB, thereby obtaining maximum performance. Our test chip had a VID of 1.3375V, but by increasing its vcore to 1.525V, we were able to boost the FSB from 333MHz (1,333MHz effective) to 418MHz (1,672MHz effective). With its bus multiplier set at nine, this overclocked the QX6850 from 3GHz to 3.76GHz, further than the QX6800, which we could only overclock to 3.6GHz.

At 3.76GHz, the QX6850 proved to be faster than an Olympic athlete on steroids and is the first air-cooled CPU to score 3.00 in our Media Benchmarks. This is an incredible achievement, given that other CPUs need to be phase-change-cooled to handle an overclock capable of achieving such a high score.

Like all Extreme Edition CPUs, the Core 2 Extreme QX6850 is considerably more expensive than a standard CPU. Just compare the prices of the processors opposite, and you’ll appreciate the premium that Intel charges for this chip. However, there’s no denying the QX6850’s awesome performance. The 1,333MHz FSB makes it a good deal faster than previous quad-core CPUs, and it overclocks further too. A Core 2 Extreme may not be for everyone but, if you have the cash and want the very best, then nothing comes close to the awesome power of the Core 2 Extreme QX6850.

Intel Core 2 Extreme QX6850 3.0GHz Socket 775 133

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