Verdict: Intel's new extreme CPU gains two more cores
Just over a year and a half ago, Intel launched the world's first dual-core desktop CPU, the Pentium Extreme Edition 840, which used the Smithfield core and was based on the NetBurst architecture.
Since then, Intel has performed a massive U-turn, ditching the NetBurst architecture in favour of the superb Core architecture. The first desktop CPU to use the Core architecture was the superlative Core 2 Extreme X6800. I say superlative because not only was this dual-core CPU ludicrously fast, but it also offered high performance per watt, and was incredibly overclockable - everything a CPU dreams of becoming when it's growing up in a silicon foundry.
Like the old Smithfield chips, the new Core 2 Extreme QX6700 simply comprises two identical cores manufactured on the same die, so while the QX6700 has four cores, it isn't the most elegant engineering solution; it's basically two dual-core cores. Although each pair of cores shares a massive 4MB Level 2 cache, no single core can address the chip's overall total of 8MB Level 2 cache.
Each of the QX6700's four cores is clocked at 2.66GHz, slightly slower than the 2.93GHz cores of the X6800.Otherwise, the two CPUs are identical and use the same 266MHz (1,066MHz effective) FSB. The QX6700's four cores mean that it has a significantly higher TDP (amount of heat generated) than the X6800 -130W vs 75W - so it requires a much more powerful cooler.
At 2.66GHz, the QX6700's performance is variable, as so few applications and games have been sufficiently multithreaded to take advantage of its four cores. In non-multithreaded applications, the QX6700's two extra cores provide absolutely no benefit.
In contrast, in fully multithreaded applications, as is the case with most media encoders, the QX6700 is amazingly quick. In our DVD encoding test, the QX6700 was an astonishing 60 per cent faster than the identically clocked dual-core Core 2 Duo E6700, and 54 per cent faster than the higher-clocked X6800. Other multithreaded applications that will see big benefits include Folding@home.
Despite the fact that the QX6700's two extra cores provide a benefit in only a few scenarios, its Core architecture base means that it shows AMD's flagship CPU, the Athlon 64 FX-62, the back of its hand in every benchmark that we ran on the two systems.
Like all Core architecture-based CPUs, the QX6700 is very overclockable and, as it carries the Extreme name, the multiplier is unlocked. By raising the multiplier from 10 to 12, the FSB from 266MHz to 300MHz and the vcore from 1.35V to 1.55V, we could benchmark the QX6700 stably at 3.6GHz. At these settings, the overclocked QX6700 set a new record in the DVD encoding test, achieving a score of 3.5, compared with 1.4 for the Athlon 64 FX-62.
The main caveat to the QX6700's performance is that it needs a very powerful cooler when it's overclocked. In our lab, we used an Arctic Cooler Freezer 7 Pro modded with a Vantec Tornado fan, but this was so noisy that a good water-cooling system is virtually mandatory.
CONCLUSION
The QX6700 is scheduled to replace the X6800 as Intel's flagship desktop CPU. As the X6800 should disappear pretty quickly, it's pretty pointless comparing the two. While the QX6700's four cores mean that it's much faster than any other chip in multithreaded applications, it's no faster than far cheaper CPUs such as Intel's £350 Core 2 Duo E6700, in single-threaded apps and games. The increase in cores means that the QX6700 is more of a niche product than the X6800, especially as it demands water cooling when it's overclocked.
As Intel is ceasing production of the X6800, the only possible competition to the QX6700 will be the forthcoming AMD quad-core system. Given how Core 2 outperforms Athlon 64, AMD has a mountain to climb if it wants to regain the CPU crown.
