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    Tech Marketing Manager HQ Array Raja@ASUS's Avatar
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    Apr 2011

    Maximus VI Series UEFI Guide for Overclocking

    This guide provides basic to advanced tips on how to overclock Haswell CPUs with ASUS motherboards. As always, we’ve incorporated a comprehensive set of auto rules for all important parameters, which makes for an easy overclocking experience.


    For overclockers, the Haswell architecture incorporates several interesting changes from previous generations:

    1) Processor related voltage rails have been moved onto the die. The motherboard supplies 1.8V via the processor socket to Intel’s on-die FIVR (fully integrated voltage regulators), which then convert the voltage down to required levels for various parts of the CPU.

    The external 1.8VDC supply is adjustable on ASUS motherboards. That’s because Intel advise the external supply should be at least 0.4V higher than processor Vcore. As overclocking requires over-voltage of Vcore, the external 1.8VDC rail needs to be able to maintain this delta under all normal operating conditions.

    When information about Intel’s shift towards integrating the power circuitry on-die were first made public, there were concerns that overclocking would be limited. That’s not the case at all. The internal power circuitry can deliver enough current to overclock Haswell beyond 7GHz (when cooled with Ln2).

    There is of course a side-effect. Having power circuitry on-die adds heat. Haswell processors run hot when voltage levels are increased. A very good air cooler is required for voltage levels above 1.15V.

    1.20V-1.23V requires use of closed loop water coolers.

    At 1.24V-1.275V dual or triple radiator water cooling solutions are advised.

    This is assuming the processor will be run at full load for extended periods of time.

    Using Vcore higher than 1.275V is not advised for 4 core 8 thread CPUs under full load as there are very few cooling solutions that can keep temps below thermal throttling point.

    However, power consumption of the processor is very low. We measured no more than 11 amperes of current draw from the EPS 12V line (about 115 Watts if we take VRM losses into account) from a 4770K clocked to 4.6GHz with 1.25Vcore under AIDA stress testing. This tells us that the high temps are purely a facet of the substrate and process size. Getting heat way from the die quickly is what matters.

    To give an idea of how good the power consumption of Haswell is under load; a few years ago I performed similar tests on Bloomfield processors (4 core, 8 thread). At 4.4GHz, Bloomfield pulled 22 amperes of current from EPS 12V (220 Watts or so after losses), that’s over double in comparison to Haswell! Haswell’s power consumption is an impressive improvement for the tech enthusiasts among us.

    At 4.6GHz, Haswell’s power consumption is a mere 35 Watts over stock frequency (not including IGP). A 700 MHz return, for a circa 35W bump in power – again impressive.

    The kicker is finding a good processor sample. Not all samples will clock to 4.6GHz with less than 1.25Vcore. The voltage variance between samples is also larger than we’ve experienced in the past – luck is needed to land a good sample!

    Given Haswell’s thermal and power characteristics, we expect enthusiasts will opt for water-cooling solutions where possible, while the die-hard crowd will likely dust off their phase change coolers. Haswell definitely benefits from lower temps and its power consumption makes this a no brainer - expect stable frequencies above 5GHz with phase change cooling on good CPUs.

    2) Unlike Ivy Bridge and Sandy Bridge, Intel have provided control over ring bus frequency for Haswell. On Sandy and Ivy Bridge, ring bus frequency was locked at 1:1 with processor core frequency. From a performance perspective, this makes sense as it means that data can be transferred between buses without waiting. Adding logic circuitry for asynchronous speeds increases design complexity and latency, so engineers are reluctant to provide such features unless there are valid reasons to do so.

    The caveat to a locked synchronous design comes when the processor is overclocked. With the ring bus frequency tied to the CPU core ratio, there’s no way of telling which of them is the limiting factor when overclocking a processor. Users provided this feedback to Intel, managing to convince engineers of the need for asynchronous operation, and we now have control over ring bus frequency.

    “Unhinging” the ring bus frequency from synchronous operation with the processor cores allows more flexibility for overclocking. The ring bus can be run slower than the processor cores, without adversely affecting desktop performance. If absolute performance is a requirement (for benchmarking), then bear in mind that keeping the ring bus frequency (cache ratio) within 300MHz of processor core frequency is adequate.

    On to the guide:

    Trust our auto rules as a starting point! We put a tremendous amount of time tuning voltages and working out parameter combinations for a wide range of processors. Take advantage of our work, and use our settings as a starting point. Tune manually as you become accustomed to the platform and the characteristics of the CPU used.

    Don’t skim read the guide!

    Don’t be afraid to ask questions if you are stuck or confused!

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