By Jake Crimmins posted Nov 14th 2011
When Intel® launched the Sandy Bridge (AKA the 2nd Generation Intel Core™ Processor Family) architecture they changed the game in overclocking, running high base clock was a thing of the past. In order to overclock Sandy Bridge to its full potential, an unlocked multiplier was needed. The new Sandy Bridge-E processors that Intel announced today (we also announced our quad-channel compatible DDR3 memory kits today) is based on the same architecture, but Intel made a key change in order to allow higher base clocks. The reason for the limited base clock adjustment was due to the link between base clock and the PCI-E/DMI Controller. Intel added the option called CPU Strap that allows the PCI-E/DMI Controller to run at a frequency near 100MHz +/-10%. You are now able to run higher base clocks however there are limitations. Along with these higher base clocks you can now also run the memory frequency much higher versus Sandy Bridge.
Since Intel added the CPU Strap option we can now run higher base clocks than 110MHz without many issues. Selecting the CPU Strap option of 125MHz will allow you to run higher base clock because it takes the base clock and divides it by 1.25 to run the PCI-E/DMI Controller at a lower frequency. The chart below shows each ratio and how to figure out your PCI-E/DMI frequency to keep it between 90MHz and 110MHz.
|Example Base Clock||CPU Strap||Math||PCI-E/DMI Frequency|
|108MHz||100MHz||108MHz / 1.00||108MHz|
|130MHz||125MHz||130MHz / 1.25||104MHz|
|170MHz||166MHz||170MHz / 1.66||102.4MHz|
|260Mhz||250MHz||260MHz / 2.5||104MHz|
I setup a system using an Intel Core i7 3960X processor on an ASUS Rampage IV Extreme motherboard. For memory I used the Corsair Dominator® GT CMGTX8 quad channel DDR3 memory kit along with a Force Series™ GT 240GB SSD. Powering the system was an Professional Series™ Gold AX1200 PSU, and I also used a Hydro Series™ H70 CORE to cool the CPU down. Let’s take a look at the bios configuration for an over clock of 4.8GHz.
You will notice the bios layout is very similar to that of a P67 or Z68 motherboard however there are a few key changes mainly the CPU Strap option. I set my base clock to 114.5MHz and set the CPU Strap to 125MHz to keep my PCI-E/DMI frequency between within the 90MHz to 110MHz range. The ClockGen Full Restart option is left enabled to give the best overclocks. The turbo ratio is set to All Cores and the CPU Multiplier is set to 42 to give us the 4.8GHz overclock. The CPU Clock Gen Filter is enabled to allow better overclocking. Finally the memory is set to run at 2442MHz which is a 42MHz overclock for the CMGTX8 modules.
For memory timings I set the values for the Dominator GT CMGTX8 memory which is rated at 10-12-10-30.
The voltages are again very similar to the P67 and Z68 motherboards however there is a second VTT Voltage and a second DRAM Voltage. The CPU Vcore voltage was set to 1.475v with the first VTT voltage set to 1.2v. The second VTTCPU Voltage was left at auto because it does not help with base clocks or memory clocks. The VCCSA voltage was set to 1.2v to help achieve higher base clocks and higher memory frequencies. Both of the DRAM voltages were set to 1.65v. Finally the PLL voltage was lowered down to 1.45v.
With memory overclocking very well on this platform compared to the previous Sandy Bridge platform, I decided to switch to a single stick of CMGTX6 to see what kind of frequencies I could run. I raised the VCCSA voltage to 1.4v and was able to run the memory without any issues at 2560MHz.
The CPU Strap option with Sandy Bridge-E has changed overclocking for the better. You can now get higher memory frequencies along with higher base clocks for the best performance.