Core i7 Extreme Overclocking with LN2
BIOS Settings and Overclocking
To overclock the 975, we wanted to find a stable starting point and work our way up to maximum frequency. The settings shown above are the ones we used to achieve a comfortable 4.22GHz overclock. From this point, we raised the host clock and multiplier to achieve higher CPU frequencies.
We are focusing primarily on CPU overclocking in this article so memory settings are kept relatively loose throughout testing. Our RAM is rated at 2000MHz 7-8-7-20 1T at 1.65V. Using high frequency DIMMs will help you during overclocking efforts as raising QPI also raised memory speed. As such, having the headroom that these sticks provide is a luxury. We used CAS 8 settings and raised tRFC to 88 in order to give us plenty of room for overclocking.
We disabled SpeedStep and CxE function within the CPU Feature menu. HT Technology or hyperthreading is left on during the benchmarks. For single threaded tests, you can disable hyperthreading and the processor should run cooler under a load and may provide higher overclocks.
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Unlike air or watercooling, using liquid nitrogen brings the added complication of temperature swing that must be controlled by pouring small amounts of LN2 in the pot from time to time. Maintaining the temperature of the pot at a certain level is the only way to assure stability throughout a benchmark. Long running tests are the most difficult to complete due to the varying degree of loads placed on the processor and the attempt to keep temperatures within the optimal range.
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Through testing, we have found that our
retail Core i7 975 achieves a stable maximum frequency between -100' to
-115'F, depending on the benchmark used. Our goal was to reach 5GHz or higher and
run a series of benchmarks to test performance.
