Intel Core 2 Extreme

Verdict: The QX6700 has four cores and is very overclockable.

In a change to its previous strategy of only producing one Extreme CPU, Intel is manufacturing two models: the Core 2 Extreme X6800 and Core 2 Extreme QX6700.

The X6800 was the first Core 2 Extreme processor, and is essentially a higher-clocked Core 2 Duo. It shares the same Conroe core as Core 2 Duo, so it has the same unified Level 2 cache design. With a 266MHz FSB (1,066MHz effective), the X6800 is clocked at 2.93GHz but, like all Extreme processors, it has a fully unlocked multiplier, so it's very overclockable. As a result, in non-multithreaded applications or those that can only take advantage of two cores, the X6800 is the fastest production CPU in the world, bar the monstrous Xeon 5160. With the right cooling, an X6800 can be overclocked to well over 4GHz, as shown in our recent cascade-cooling feature (see Issue 39, p118). However, cheaper standard Core 2 Duo CPUs are just as fast in games.

The second Core 2 Extreme to appear was the QX6700, the world's first quad-core processor designed for desktop PCs. Essentially, it's two Core 2 Duo E6700 cores packaged together in one CPU die, so unfortunately, although each pair of cores has a unified 4MB Level 2 cache, no one core can access all 8MB of Level 2 cache. The Q6700 runs at the same frequency as that of the E6700 (2.66GHz with a 1,066MHz effective FSB), although, like the X6800, it has a fully unlocked multiplier, so it's very overclockable. However, with a TDP of 130W, it produces far more waste heat than any other Core 2 CPU, and needs to be water-cooled when overclocked. As the QX6700 runs at a slightly lower clock speed than the X6800, it's slower in non-multithreaded applications. However, in multithreaded applications, or when running lots of applications together, its performance is unparalleled.

As with the Athlon 64 FX-series, both Core 2 Extreme CPUs are shackled by a hefty price premium, although this is justified to some extent by their incredible performance and overclockability. If you've just won the lottery or have an incredibly rich relative, nothing bar a pair of Xeon 5160s can touch the X6800 or QX6700 for brute performance.

Click here for full details of the Intel Core 2 Extreme family.