4 GHz...Barely: Pentium 4 Extreme Edition
The 4 GHz in the Pentium 4 Extreme Edition is a beautiful sight.
We had some luck with this Pentium 4 EE, as it is one of the rare examples of a processor that didn't have a set multiplier. We discovered that fact when we accidentally booted the test system several weeks ago with a 4.2 GHz processor (earlier, we had used a P4 with 3.06 GHz, which employed the same multiplier).
We then discovered that 4 GHz is the upper limit for this processor. Beyond that, the system no longer works. Such a high clock rate in the P4 EE deserves its fair share of credit, as processors with increasing cache are more sensitive to clock increases. They also have little tolerance for overclocking.
Considering the fact that the Extreme is a processor based on the relatively old 130 nm technology, 4 GHz is impressive. As a comparison: Intel's road map doesn't envisage 4 GHz processors before the fourth quarter of this year.
The P4 processor we used allowed for a free selection of the multiplier. At a 200 MHz clock rate, x20 results in the said 4 GHz.
Ideal timings: The fast memory module allows for stable operation of the Intel system with CL2-2-2-5.