|Intel X79 Motherboard Overclocking Guide
| Written by Juan Jose Guerrero III - ASUS
|Thursday, 29 March 2012
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General Overclocking Recommendations
Setting internal PLL overvoltage
- Internal PLL is currently not present within our UEFI due to internal analysis showing no benefit in CPU frequency scaling. In addition changes to CPU architecture have incorporated this setting directly into CPUs own auto rules.
Consideration of power states (Cstates)
- Internal analysis has confirmed that for general overclocking C States do not have an effect on multiplier scaling.
In most situations you can maintain C1E, C3, C6 and C7 enabled and be able to maintain CPU frequency related scaling. Keep in mind that if you are using a manual vid you are NOT going to have a reduction in CPU vid even with speedstep enabled. It is advised for overclocks between 4.4 - 4.6GHz to use an offset vid without the use of LLC. This voltage configuration will provide a great mix of reduced idle and load temperature, extended CPU lifespan as you are not forcing additionally a consistent frequency, voltage to the CPU as well as minimizing heat output. In addition the offset voltage will track the VRD and apply an offset voltage amount to the vid value defined by the multiplier.
- When exceeding 4.8GHz it is advised you consider disabling power/ C states so as to not add complexity to the overclock. In addition disabling of C States is advised at this stage as C state values (C3 through C7) may potentially induced cold post/cold boot issues (such as instability)
Consideration of CPU specific features
- Internal analysis has confirmed that for general overclocking CPU specific features like Virtualization, Execute Bit Disable do not have an effect on multiplier scaling.
In most situations you can maintain these options enabled and be able to maintain CPU frequency related scaling.
When exceeding 4.8GHz it is advised you consider disabling virtualization and other like features so as to not add complexity to the overclock.
Considerations on how to scale CPU frequency. (Multiplier, BCLK / Strap)
- Sandy Bridge E and the X79 introduce a new option outside of standard BCLK and Multiplier adjustments. As part of CPU design and architecture there is the inclusion of an external clock generator that enables a CPU Strap. This strap delinks the CPU from its attached buses to allow for new BCLK settings. This offer a higher potential maximum OC relative to multiplier x BCLK. In addition adjustment to the CPU strap provides the benefit of providing additional memory dividers.
An example of this is defining a 125 BCLK / Strap value will provide a 3.9GHz with support for a 2000 memory divider which is not present at the default 100 BCLK / Strap value.
- In internal analysis we have found the all CPUs will run the 100 and 125 BCLK / Strap values. When exceeding 125 and attempting 166 BCLK / Strap value we have found considerably less CPUs capable of initializing this value. As such straps of 166 or greater are not recommended.
- In addition when attempting to scale BCLK the same limitations are present as previous generation platforms. As such scaling of approx 3 to 5 BCLK is all that is available. ASUS does offer specialized options that can potentially exceed BCLK scaling BCLK Skew. When considering a combination of BCLK with a BCLK/ Strap will still carry the same limited BCLK scaling range.
- Due to restrictions with BCLK and BCLK / Strap it is advised that overclocking be achieved through the use of multiplier adjustments only. That being noted ASUS has optimized auto rule parameters to support either configuration mode or both.
- It is advised once exceeding 46x multipliers to consider PerCore overclocking. This can provide higher frequency performance relative to threaded load but offers the advantage of not requiring additional vid or producing additional heat out or increasing power draw.
An example is:
- 5 and 6 cores - 46x
- 3 and 4 cores - 47x
- 1 and 2 cores - 48x
Other variations of this type of configuration are possible including higher single thread multi values such as 49 or 50.
CPU frequency speeds for corresponding straps:
- 34x with 125 = 4250
- 35x with 125 = 4375
- 36x with 125 = 4500
- 37x with 125 = 4625
- 38x with 125 = 4750
- 39x with 125 = 4875
- 40x with 125 = 5000