The Pentium Extreme Edition based on the dual-core Pentium D branded Presler was introduced as the 955 model, at 3.46 GHz, and used a 1066 MT/s FSB compared to the 800 MT/s in the non-Extreme edition. A second version, the 965 at 3.73 GHz followed in March 2006. Both CPU's also feature Hyper-Threading Technology. Many overclockers, however, had been able to overclock the core to 4.26 GHz using air cooling simply by raising the unlocked CPU multiplier. The 'Presler Extreme Edition' would run only combined with the Intel 975X chipset (it could also work with the 955X chipset, though this combination was not supported by Intel). The i975X featured the ICH7R southbridge and supported all LGA 775 (Socket T) Pentium 4, Pentium D, and Pentium Extreme Edition branded processors.

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Source[ Wikipedia ]