Intel X79 Motherboard Overclocking Guide

By Juan Jose Guerrero III
Reproduced with permission, courtesy ASUS

This document is meant to assist and outline aspects of overclocking parameters as well as the experience of overclocking on the ASUS X79 series of motherboards. I have detailed our recommendations to maximize the overclocking potential / scaling on ASUS' X79 series of motherboards. This guide has been developed after extensive internal testing across multiple boards, multiple UEFI builds and a high sampling rate of C0 CPUs and limited sampling of C1 stepping CPUs. While this guide is not definitive and will not contain every possible overclocking combination or guarantee results, the information detailed has been consistently duplicated and yielded repeatable results in our testing. Of course the quality of the CPU and cooling is very important but overall we think the results on our boards should exceed those of others at like settings.

A couple of key items to first be aware of prior to getting into specifics are

• Final Intel MRC code was only recently released as such the UEFI builds we are providing do include it but will be continuing to refine and improve performance and compatibility over the coming month. Due to the nature of memory training during the post and initialization process and use of high density and high dim counts this aspect of memory training is a key aspect to be aware of. The memory training process can affect and even change the initial stability or boot stability of a platform and is more likely to present itself in higher density configurations especially at higher frequencies where there is less variance accepted in high density modules. In addition the variance relative to IMC performance/scaling and the margin/delta present between CPUs needs to also be kept in mind; as such dram divider scaling in excess of 1600 is not advised prior to validation of the scaling being achieved at lower or stock multipliers. For more information relative to memory training parameters please reference the memory training adjustment option of this guide.
  
• Due to the logical high core count and hyper threading be aware that strong cooling is required for 4.5GHz + overclocking. For 4.8GHz and upwards you will need a solution that can dissipate in excess of 175watts (with 180 to 200 watts being realistic under synthetic stress tests). When attempting or exceeding 5.0GHz with high vid and non recommended synthetics like prime 95 or AVX coded Linpack libraries heat production can easily exceed can 200-205 watts. Be advised that relative to these wattage levels draw on your PSU can be very high and a PSU with a minimum of a quality 25amp rail if not 30amp rail is strongly recommended. In addition please factor in efficiency of the power supply as it will be affected over time and dependent on ambient / operating temperature. High Efficiency PSUs are recommended (80% Silver or preferably 80% Gold in addition if possible validation support for advanced C State protocols (C6, C7)
  
• Unvalidated stress tests are not advised (such as Prime 95 or LinX or other comparable applications). For high grade CPU/IMC and System Bus testing Aida64 is recommended along with general applications usage like PC Mark 7. Aida has an advantage as it is stability test has been designed for the Sandy Bridge E architecture and test specific functions like AES, AVX and other instruction sets that prime and like synthetics do not touch. As such not only does it load the CPU 100% but will also test other parts of CPU not used under applications like Prime 95. Other applications to consider are SiSoft 2012 or Passmark BurnIn. Be advised validation has not been completed using Prime 95 version 26 and LinX (10.3.7.012) and OCCT 4.1.0 beta 1 but once we have internally tested to ensure at least limited support and operation.

Approximate wattage per application (approx 4.8GHz)

3D Engine - 85-100 Watts

Video Playback (Various formats) - 45-65 watts

Music Playback (Various formats) 30-45 watts

Multitasking (Email Client, Photoviewer, Webvideo, Music) - 65 -75 Watts

Aida64 - 160+ Watts

Prime95 Large FFT - 180+ watts

• CPU Margin is an important factor to consider, in internal testing we have found a wide range of frequencies that CPUs can attain this is relative to both Core Frequency as well IMC controller performance (frequency of memory divider). This is an important factor when overlocking as VCCSA voltage may require additional adjustment relative to the density and frequency used. Keep in mind this will also affect overall heat output and total power draw. For testing inside a chassis DRAM can also actively heat up the ambient CPU socket area, as such keep airflow and adequate cooling in mind.
  
• Due to tight VRM package design as imposed by the large CPU socket VRM cooling is a key aspect to consider when attempting overclocking. Please ensure you have a reasonable amount of CFM and indirect or preferred direct airflow for the primary VRM heatsink assembly and if possible the VRM backplane. Recommended CFM would be at least 30CFM with a range up to 45CFM anything in excess of this greatly will help to stabilize and ensure superior overclocking scaling and stability. (Maintaining lower VRM temperatures will help to ensure superior and higher consistent power delivery which is key as the board and CPU are push to higher frequencies) Be advised should you not adequately cool the VRM heatsink assembly at high enough frequencies and for a long enough period of time the VRMs high operating temperature could induce CPU throttle and or CPU cores/threads to drop under load or a general shutdown/stop error. Overall increase consistent high VRm temperatures (90c plus are not advised.
  
• Intel's inclusion of a Gear Ratio (Strap) allows for flexibility in CPU and Dram scaling. In most situations the standard recommendation of sole multiplier scaling is advised. In certain situations the strap may be a preferred option. For most CPUs there is only an approximate 5 to 10% range of adjustment/variation for the PCIE/DMI controller. As such you need to stay close to the defined straps. Be advised ASUS has tuned auto rules to generally not need you to manually define the strap.

BCLK and CPU Strap Link detailing

CPU has 4 straps: 100, 125, 167, 250: 1:1, 1:1.25, 1:1.67, 1:2.5 respectively

• When you select 125MHz BCLK with 125 strap, 125mhz is given to CPU and internally it gives its own PCIE/DMI Controller 125 / 1.25 = 100MHz.
• When you select 129MHz BCLK with 125 strap, 129mhz is given to CPU and internally it gives its own PCIE/DMI Controller 129 / 1.25 = 103.2MHz.
• When you select 122MHz BCLK with 125 strap, 122mhz is given to CPU and internally it gives its own PCIE/DMI Controller 122 / 1.25 = 97.6MHz.

When needing a memory divider in excess of 1866 like 2000 but less than 2133. The Strap will allow for a wide range of default operating dividers/frequencies.

In addition when potentially higher multipliers have weaker load tolerances a combination of strap with multiplier may yield superior stability.

• As part of the post process memory training occurs this process occurs each time the system posts and boots. As such the MRC defines new memory training information which can potentially affect stability at higher DRAM frequencies and overclocks. This is an important aspect to keep in mind as it can "destabilize a thought to be stable overclock" ASUS has incorporated advanced control parameters to help maintain memory training parameters that have yielded stable results. These are hosted under DRAM timings some of these values are Transmitter/Receiver slew. These values along with other specific sub timings can be key in helping to define improved scaling and stability with higher density modules (4GB DIMMs) especially at higher dividers/frequencies.

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