Overclocking and Power Consumption
We also spent some time overclocking our Core i7-3960X Extreme Edition sample using Intel’s own DX79SI motherboard and the Asus P9X79 Deluxe, with similar results.
Like the first batch of Sandy Bridge-based second generation Intel Core processors, new Sandy Bridge-E based processors offer limited flexibility when overclocking via BCLK manipulation. If you want to tweak CPU and memory frequencies via the BCLK, it can only be increased by a few MHz (think 3-5MHz) maximum.
However, with Sandy Bridge-E, two new BCLK multiples or straps are also available, that were not offered on earlier Sandy Bridge processors. With Sandy Bridge, only a 100MHz BCLK is available, but with Sandy Bridge-E 100MHz, 125MHz, and 166MHz BCLK frequencies are also possible. In addition, like K series SKUs, the Core i7-3960X Extreme Edition is fully unlocked; so CPU, Turbo, and Memory frequencies can be easily altered through multiplier manipulation as well.
With a chip as large and complex as the Intel Core i7-3960X Extreme Edition, power and cooling considerations are very important when overclocking. At its stock configuration the Core i7-3960X is a rated for 130W, but power consumption and heat output can shoot up considerably when the chip is pushed well beyond spec. As such, Intel has incorporated options to increase voltages and specify peak current thresholds too. The new options and power / heat considerations add some wrinkles and complexity to the overclocking process, but we still found overclocking SBE to be quite easy and very fruitful.
Using Intel’s RTS2011LC thermal solution, we were able to take our particular Core i7-3960X Extreme Edition processor all the way up to 4.75GHz using a 125MHz BCLK and a peak all-core Turbo multiplier of 38. At that speed, however, we were pushing the limits of the RTS2011LC thermal solution as the processor would approach the 90ºC mark after long periods of sustained load. At 91ºC, the chip will begin to throttle. At 4.75GHz, the Core i7-3960X Extreme Edition processor put up a Cinebench 11.5 MT score of 13.89.
We also spent some time using the “easy” overclocking tools available on Intel’s and Asus’ X79 boards with success. Hitting the “High Performance” performance option on Asus’ board, for example, yielded a peak CPU frequency of about 4.2GHz, with only a single click in the UEFI. And at that speed, the chip barely broke a sweat, running at about 75’C under load.
Before bringing this article to a close, we'd also like to take a but about power consumption. Throughout all of our benchmarking and testing, we monitored how much power our Intel Core i7-3960X-based test system was consuming with a power meter, versus other test systems we used for benchmark comparisons on the previous pages. Our goal was to give you an idea as to how much power each configuration used while idling at the Windows desktop and while under a heavy CPU workload. Keep in mind, this is total system power consumption being measured at the outlet and not the the individual power of the CPUs alone.
The Core i7-3960X ended up consuming somewhat less power than the six-core Core i7-990X under both idle and load conditions, but considerably more than the quad-core Core i7-2700K. The Core i7-3960X's idle and load power was also somewhat higher than the AMD FX-8150, but considering the massive performance increases offered by the Core i7-3960X, using a bit more power is easily justified.
As we mentioned earlier, overclocking the Core i7-3960X can result in large increases in power consumption. To demonstrate this, we also monitored power consumption with the chip running at its stock configuration and while overclocked to 4.2GHz and 4.7GHz. As you can see, power consumption jumped up almost 200 watts with the chip overclocked to 4.7GHz.