We received from Intel a Core 2 Extreme QX6850 engineering sample, which is now the most high-end desktop CPU available on the market today, featuring four cores, running at 3 GHz internally and 1,333 MHz externally – a new clock rate that will be officially introduced tomorrow morning. Since our engineering sample had its clock multiplier unlocked, we were able to increase its clock multiplier from 9x to 10x, simulating a future quad-core CPU running at 3.33 GHz – a “Core 2 Extreme QX 6950”. We compared this new CPU to several other CPUs from Intel, check it out.

Core 2 Extreme QX6850Figure 1: Core 2 Extreme QX6850 engineering sample.

Intel will release tomorrow morning some new CPUs using the new 1,333 MHz external bus. This new external bus works at 333 MHz transferring four data chunks per clock cycle, and that is why it is referred as 1,333 MHz (333 MHz x 4). In reality it doesn’t work at 1,333 MHz. CPUs using this new bus will use the number “50” at the end of its model name.

Core 2 Extreme QX6850 works internally at 3 GHz multiplying its 333 MHz external bus by 9 and has two 4 MB L2 memory caches. Its full specs you can see in Figure 2. Keep in mind that Core 2 Extreme QX6800, a quad-core CPU with similar model numbering, has slightly different specs as it works internally at 2.93 GHz (11 x 266 MHz), not 3 GHz like QX6850.

Core 2 Extreme QX6850Figure 2: Core 2 Extreme QX6850 specs.

Since our engineering sample had its clock multiplier unlocked, we were able to configure it at 10, making our CPU to run internally at 3.33 GHz, as you can see in Figure 3. We could run flawlessly all our programs under this configuration, so we included the results of our CPU running under this scenario in order to simulate a future “QX6950” CPU. We put this naming inside quotes because this CPU doesn’t exist yet, we don’t know if Intel will actually release it and even if Intel does we can’t assume that this is the name that they will use for this CPU.

Core 2 Extreme QX6850Figure 3: “Core 2 Extreme QX6950” specs – our CPU with a 10x clock multiplier.

Because this CPU is based on the new 1,333 MHz FSB, it requires a motherboard supporting this new FSB. So you won’t be able to install this or any other CPU based on the new 1,333 MHz external bus on older socket LGA775 motherboards, meaning that you probably won’t be able to upgrade your CPU with a new one by just replacing the processor, you will probably need to replace your motherboard as well.

Intel P35 and NVIDIA nForce 680i or 650i chipsets are some of the chipsets that support the new 1,333 MHz FSB. In our review we used a MSI P35 Platinum motherboard, which is based on the new Intel P35 chipset, but we faced a problem with this motherboard during our tests that we need to explain.

We were using DDR2-1066/PC2-8500 memories and we tried to keep them always running at 1,066 MHz, however this was only possible when the CPU external clock was of 1,066 MHz. With other clock rates the motherboard didn’t provide a memory clock multiplier that resulted in 1,066 MHz. With the FSB set at 800 MHz – which was necessary by our Pentium 4 3.4 GHz – the maximum clock rate we could set for our memories was also 800 MHz. For Core 2 Duo E6750, Core 2 Extreme QX6850 and our QX6950 simulation we had the option to set our memories at 800 MHz, 1000 MHz, 1110 MHz or 1333 MHz. We tried to keep them at 1110 MHz but the system was unstable, thus we set them at 1000 MHz, 66 MHz below the clock rate they should be running at. This slight difference shouldn’t impact the final results.

In the table below we summarized below all CPUs included in this review with their main specs. We also added a column called “memory clock” for you to know the clock rate our memories where running when we collected data for each CPU – the clock rate below 1,066 MHz was a limitation from the motherboard we were using.

CPU Cores Internal Clock External Clock L2 Memory Cache Platform TDP Memory Clock
Core 2 Extreme “QX6950”  4 3.33 GHz 1,333 MHz (333 MHz x 4) 4 MB x 2 Socket LGA775 130 W 1,000 MHz
Core 2 Extreme QX6850 4 3 GHz 1,333 MHz (333 MHz x 4) 4 MB x 2 Socket LGA775 130 W 1,000 MHz
Core 2 Extreme QX6700 4 2.66 GHz 1,066 MHz (266 MHz x 4) 4 MB x 2 Socket LGA775 130 W 1,066 MHz
Core 2 Extreme X6800 2 2.93 GHz 1,066 MHz (266 MHz x 4) 4 MB Socket LGA775 75 W 1,066 MHz
Core 2 Duo E6750 2 2.66 GHz 1,333 MHz (333 MHz x 4) 4 MB Socket LGA775 65 W 1,000 MHz
Core 2 Duo E6700 2 2.66 GHz 1,066 MHz (266 MHz x 4) 4 MB Socket LGA775 65 W 1,066 MHz
Pentium 4 550 1 3.4 GHz 800 MHz (200 MHz x 4) 1 MB Socket LGA775 115 W 800 MHz

Unfortunately Intel didn’t provide us a Pentium D or a Pentium Extreme Edition samples for reviewing, and AMD seems to be out of samples and new high-end CPUs, because we haven’t received new samples from them for ages. A pity. If you’d like to see a comparison between the reviewed CPUs and Athlon 64 X2 5000+, please read our Core 2 Extreme QX6700 Review.


Gabriel Torres is a Brazilian best-selling ICT expert, with 24 books published. He started his online career in 1996, when he launched Clube do Hardware, which is one of the oldest and largest websites about technology in Brazil. He created Hardware Secrets in 1999 to expand his knowledge outside his home country.