Intel Sandy Bridge-E Review - Core i7-3960X and X79 Chipset Tested
Overclocking with the new Sandy Bridge-E processors is almost exactly the same as it is with current Sandy Bridge parts- with just a couple of tweaks that increase OC potential.
As we mentioned on the previous page, the new lowest multiplier for the CPU is 12x, lowering the idle speed to 1200 MHz compared to the 1600 MHz on the previous generation.
With only a couple of threads running, the Core i7-3960X will spike as high as 3.9 GHz using the standard Turbo Boost technology which provides a noticeable increase in performance over the 3.3 GHz base clock.
With all cores loaded though, the highest clock speed provided by this Extreme Edition CPU is 3.6 GHz.
This is a screenshot from the BIOS of ASUS' latest UEFI for the X79 platforms. You can see that the Base Clock (BCLK) starts at 100 MHz and the Turbo ratio can be adjusted for all cores (giving us a consistently clocked part) or for each core (performing more like the Intel default actions). This is exactly the way current Sandy Bridge overclocking works.
What is new is the addition of the "CPU Strap" - though it is called different things in different motherboard BIOSes. This is essentially a new multiplier added to the Sandy Bridge-E processor that allows the BCLK to be set higher than it could be on Sandy Bridge. If you have overclocked with SNB previously, you know that pushing beyond the 100 MHz BCLK was very difficult: if you could get 107-108 MHz you were doing very well. With the CPU Strap, you can now actually run at higher BCLK settings.
Setting the CPU Strap to 1.25x or 125 MHz will actually start the CPU at 125 MHz BCLK and then let you adjust from there if you want. You will still only get the minimal stable adjustments (7-8 MHz) but you'll then be running at 130+ MHz BCLK and when coupled with your multiplier adjustments, could lead to your best performing system.
The CPU Strap keeps the other multipliers in check as well - you don't have to worry about increasing the speed of your memory or PCI Express clocks when using the strap settings. That was really the bottleneck on current Sandy Bridge systems, and Intel has helped resolve this with Sandy Bridge-E. Chances are good though that you'll still be able to hit a really good overclock using JUST the multipliers if you have the Core i7-3960X or the Core i7-3930K as they are fully unlocked. The CPU strap could be much more interesting with the "partially unlocked" Core i7-3820 when it arrives.
If you happen to purchase an Intel DX79SI they also permit overclocking to higher degree than you might, at first, have guessed both in the BIOS and with a highly competent software overclocking suite called XTune.
Using the Core i7-3960X and our Intel sealed loop water cooler I was able to hit a clock speed of 4.7 GHz, stable, on all 6-cores. For those highly threaded applications that would normally be capped at 3.6 GHz, that is a 1.1 GHz overclock (just over 30%) - very nice!!
You can see our POV-Ray benchmark result running under these settings is incredibly high as well - compared to the score of 7506 pps at default speeds.