Motherboard vendors have been touting 1333MHz front side bus (FSB) support for their latest motherboards in preparation for Intel's new line of CPUs and, finally, a CPU that can run at this speed has been introduced. Users running a motherboard with an Intel 3-series chipset (such as the P35) or a board with an NVIDIA nForce 680i chipset, will be able to plug in the Intel Core 2 Extreme QX6850 quad-core CPU, which has a 1333MHz front side bus (FSB) and a 3GHz clock speed.

The 3GHz clock speed is currently the fastest in the Core 2 range with the previous fastest being Intel's 2.93GHz QX6800. Until now the most a Core 2 CPU could offer was a 1066MHz front side bus. The QX6850, on the other hand, is made with DDR3-based motherboards in mind, and only motherboards running DDR3 1333MHz RAM will be able to realise the full potential of the new CPU. However, the Qx6850 will also run with slower DDR3 memory -- 1200MHz and 1066MHz, for example.

DDR2 isn't entirely out of the frame just yet, however, and many boards that have chipsets capable running the QX6850 also come with DDR2 slots. Intel says that users with P965-based motherboards will not be able to run CPUs with a 1333MHz FSB speed because the 965 chipset isn't validated to run at that speed. Users with P965-based boards should check their vendor's Web site to make sure though, as some motherboards based on the P965 chipset can indeed handle the QX6850.

The QX6580 is a 65 nanometre product, so it shares similar thermal characteristics with the other Core 2 products that are available, and it's a quad-core CPU, so it's perfectly suited to severe multitasking and running multithreaded applications. Indeed, only extreme users will be able to maximum out this Extreme CPU; it's one that should definitely be considered for a video editing machine or a high-end gaming rig.

Testing with a Gigabyte P35 chipset-based motherboard (the P35T-DQ6) and 2GB of Samsung DDR3 memory, the QX6850 showed good speed in our benchmarks and it was reliable all throughout our testing phase. With our DDR3 memory running at 1333MHz and the QX6850 at 3GHz, WorldBench 6 scored a nifty 117, which this three points more than it scored when the memory was set to 1066MHz. The two applications that benefited from the extra memory bandwidth were WinZip and Firefox, but only slight differences were evident in the media encoding tests. This was also reflected in our Cdex and iTunes encoding tasks, where the extra memory bandwidth had no effect. At 3GHz, the QX6850 was able to compress 53min worth of WAV files to 192Kbps MP3 files in just 1min 29sec using Cdex, and it compressed those same WAV files to 56Kbps MP3 files in just 39sec using iTunes.

Using the standard Intel cooler, we were able to reliably overclock the QX6850 to 3.6GHz, where it recorded the fastest WorldBench 6 score we've seen thus far -- 128. The extra speed cut down the time it took to encode MP3s in Cdex by 15sec and in iTunes by 8sec. We overclocked the CPU by changing its clock multiplier, which is unlocked (only Intel Extreme CPUs are unlocked). Users with more advanced CPU cooling and stable memory sticks may also be able to run a faster FSB speed than 1333MHz and reach greater clock frequencies.