Reaching The Goal
A little more testing revealed 4.9 GHz at 1.60V and new thermal stability limits. Even the slightest increase voltage would cause our CPU to reset at 39° Celsius, and even the slightest increase in speed would lower the temperature at which our CPU reset. We had to get our temperatures down.
Reports from several cooling sites show that the latest compounds can reduce temperatures by up to 4° compared to Zalman’s ZM-STG1, yet our testing showed that a drop of at least 10° would be required to reach full CPU stability at 5 GHz. The logical next step would have been to smooth the evaporator’s mating surface through processes such as precision sanding and lapping, but we weren’t certain how thick this surface was and didn’t want to risk damaging a borrowed product.
We finally reached our 5 GHz goal not by increasing thermal transfer speed, but by reducing heat. Disabling Intel's Hyper-Threading technology dropped us from twelve logical to six physical cores, while simultaneously dropping CPU temperatures by nearly 20°.
The Core-i7 980X has completely unlocked multipliers, yet no multiplier exists to reach 5 GHz at the stock 133 MHz base clock. We also wanted to retain a consistent memory data rate to assure accurate assessment of CPU performance. Increasing our base clock from exactly 133.333 to 166.666 MHz would have been a perfect solution, using a CPU multiplier of 30 and a DRAM multiplier of 4 to reach 5.00 GHz and DDR3-1333. Gigabyte doesn’t use fractional base clock frequencies however, so the actual base clock was increased from 133.0 to 166.0 MHz.