Lynnfield die is not very different from Bloomfield. True, these processors are mad with the same manufacturing process and their major units are the same. Therefore, it would be strange if the overclocking potential of the freshly announced LGA1156 processors could be very different from that of LGA1366 CPUs. Nevertheless, to check out this hypothesis we performed a number of overclocking experiments of the Core i7-870 and Core i5-750 processors.
The tests were performed on a Gigabyte GA-P55-UD6 platform. The CPU was cooled with Thermalright MUX-120 solution with traditionally curved base plate and Enermax Magma UCMA12 fan (1500 RPM). System stability under load was tested using LinX 0.6.3 utility.
There is only one way to overclock LGA1156 processors: by raising the BCLK clock generator frequency. This is when the Uncore frequency increases together with the CPU core clock. However, there is nothing you can do about it, because Lynnfield processors have not only a locked clock frequency multiplier but also a locked multiplier for the Uncore frequency. The memory frequency increases together with BCLK, but luckily its multipliers can be lowered.
When we tried to overclock Core i7-870 processor we managed to achieve full stability at 4.07 GHz.
To achieve this result we had to increase the processor core voltage to 1.4 V, which is a relatively safe level for Lynnfield, provided there is proper cooling. However, in our case CPU core temperature reached 93 °C. And although it is a really high temperature, the CPU remained absolutely stable and didn’t overheat. So, CPUs from Core i7-800 family can really work at 4 GHz frequency with air cooling, just like their elder brothers from the Core i7-900 series.
The second part of our experiments dealt with Core i5-750 processor. This CPU doesn’t support Hyper-Threading technology, which leads to its lower temperature under full load. We hope that this peculiarity of the Core i5 will make its overclocking more successful. However, on the other hand, Core i5-750 has a lower clock multiplier, which requires increasing the BCLK frequency during overclocking to higher levels. Luckily, the maximum BCLK frequency of 210-215 MHz that we saw on typical LGA1366 platforms, can be easily surpassed on LGA1156 platforms.
However, we didn’t have to increase the BCLK frequency beyond 210 MHz. Our Core i5-750 sample could work stably only at 4.1 GHz, which only needs 205 MHz BCLK.
The core voltage was increased to 1.4 V, but the temperature of the overclocked processors didn’t exceed 81 °C. So, it appears that despite relatively small difference between the overclocking results of Core i7-870 and Core i5-750, the temperature of a processor without Hyper-Threading support is actually way lower under maximum load. And it means that during overclocking experiments with Core i5-750 we can also use relatively inexpensive cooling systems.
I have to say that we performed our overclocking experiments with dynamic multiplier adjustment via Turbo Mode disabled. However, I have to admit that overclocking with enabled Turbo Mode is pretty interesting, too. It is quite possible that in case of low computational load on the CPU, its frequency may be increased higher than we managed to achieve today. Therefore, very soon we are going to publish a new article where we will discuss in greater detail all aspects of LGA1156 processors overclocking.