Complete BIOS Tuning Guide - "Over Voltage" (Cont'd)

CPU GTL_REF(0~4) Ratio - [Auto, Default, -226mV ~ +224mV] Gunning Transceiver Logic (GTL) voltages are nothing more than reference thresholds used by the CPU and SPP (MCH) in determining if the voltage potential on a FSB data or address signal line is intended to represent either a logic level 1 (high) or logical level 0 (low). These voltages are generated by the motherboard, usually though the use of precision voltage dividers or high-accuracy, programmable digital potentiometers. Although the most common way to specify these values is as a percentage (or ratio) of full scale CPU VTT Voltage, NVIDIA has decided to provide these settings as simple offsets meaning a little math will be involved if you want to make a change.

These reference values are particularly important when overclocking quad-core CPUs, especially when venturing above about 475MHz FSB. The ability to tune these values per die can mean the difference between achieving a stable overclock at 475FSB and one at 500FSB. The real power seen in GTL reference tuning comes in the ability to provide each quad-core die with separate reference values. (Recall that current quad-cores from Intel are an MCM design consisting of two dual-core dies on a single substrate package.)

This can get tricky though as each die receives two GTL reference voltages - one for the FSB Data Bus (running at the full FSB transfer rate) and one for the FSB Address Bus (running at half the FSB transfer rate). This means CPU GTL_REF0 Ratio is for the Core 0/1 Data Bus, CPU GTL_REF1 Ratio is for the Core 2/3 Data Bus, CPU GTL_REF2 Ratio is for the Core 0/1 Address Bus, and CPU GTL_REF3 Ratio is for the Core2/3 Address Bus. CPU GTL_REF2 Ratio and CPU GTL_REF3 Ratio will have no affect with a dual-core CPU installed, in which case CPU GTL_REF0 Ratio is for the Core 0/1 Data Bus and CPU GTL_REF1 Ratio is for the Core 0/1 Address Bus. As a rule, adjustments are normally made to FSB Data Bus values first. These lines are consistently heavily loaded and as such are more susceptible to the detrimental effects of reduced signaling margins.

Intel's GTL specification dictates that each reference voltage should be tightly controlled as 67% of the current VTT voltage (0.67 times CPU VTT Voltage). Typically, changes in VTT are automatically compensated with standard voltage divider circuits dedicated to the generation of each GTL reference voltage. Historical data has shown that dual-core CPUs (in particular 45nm dual-cores) often clock to higher FSB levels when the GTL reference values are closer to 63 ~ 64% of VTT while quad-core CPUs usually need the full strength value or even a little more voltage (67 ~ 70% of VTT).

As an exercise in the application of basic math, consider the following. With VTT at 1.10V, the GTL reference voltages at 67% would be 0.737V (0.67 times 1.10V). If VTT increased to 1.26V, the new GTL reference voltage would be 0.844V, calculated the same as before. If we wanted to adjust this down to 63%, we would simply multiply the current VTT voltage by the difference between the actual and desired percentages of full scale VTT (67% minus 63% equals 4% or 0.04) and then convert this to mV by multiplying by 1000. At 1.26V, the result would be 50mV and since we want to reduce the GTL reference voltage we would pick the value closest to -50mV. Sometimes tweaking VTT slightly up or down can help if none of the available values is close enough the desired offset. Of course, you will need to repeat the calculation using the new VTT.

Proper GTL reference level tuning can sometimes allow for a dramatic reduction in VTT and in some severe cases even permits the use of a lower core supply voltage (Vcore). The most recent x64 build of Prime95, version 25.6 build 6, provides an excellent means for testing the effectiveness of CPU-specific GTL tuning. Simply load the program, select the Blend type Torture Test, and watch for any instance to drop out. Note the instance number (which will correlate to the core in question), reset and enter the BIOS, make a small adjustment to the corresponding GTL reference value(s), and then start a new test run. If the test runs for a longer period of time then you can be confident that you are at least moving in the right direction. Continue this process until the system is sufficiently stable with the current settings.

Those that want to know more about GTL reference voltages and related tuning issues are encouraged to carefully examine more in-depth articles on the subject posted here and here.

NB GTL_REF Ratio - [Auto, Default, -126mV ~ +160mV] The NB (SPP) GTL reference voltage provides the same functionality as those for the CPU, the only difference being that the Northbridge uses only a single value. Tuning in the right GTL reference voltage (usually near the nominal 67% value) can sometimes lead to lower stable VDIMM requirements.

DDR3 CHA(1~2)/CHB(1~2) Ref Voltage - [Auto, Default, -126mV ~ +160mV] These voltages work like GTL references for memory, except that VTT for the memory is defined as one-half VDIMM. Small adjustments in either direction can sometimes bring additional stability or higher memory overclocks; however, testing the effectiveness of any change is exceedingly difficult and time consuming. Most of the time these are better off simply left on Auto.

Complete BIOS Tuning Guide - "Over Voltage" Complete BIOS Tuning Guide - "CPU Configuration"
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  • Rodriguez - Friday, June 20, 2008 - link

    Can anyone here indicate how to reach FSB 500 (2000) with Striker II Extreme & QX9770 C1, most I can get is 1900FSB.

    I've seen Kris reach this speed in this article & was eager to get to this speed as soon as I received my new CPU, but it has been more difficult than I thought, I was sure that if with my previous Q6600 G0 y could easily get 1900/1950FSB, now with QX9770 would be peanuts. The main reason I bought this CPU was to run 2000FSB linked & synced with Ballistix 2000 SLI.

    Please give all detailed BIOS setup options for this CPU if possible

    Nobody in Asus forum using this setup has been able to reach 2000FSB, but I have seen a few reviews (like Anandtech's) & posts showing it's possible

    By the way, memory has been tested unlinked at 2000Mhz 9-8-8-24, 1.9v P1/P2 Enabled & works great


    QX9770 rev. C1 3.2Ghz (watercooled)
    Asus Striker II Extreme BIOS 801, ver 1.02G (watercooled)
    PC Power & Cooling Turbo Cool 1200W
    4 x 1GB Crucial Ballistix PC16000 SLI EPP2 , 2000Mhz 1800 8-7-7-24- 1T - 1.9v
    SLI Leadtek PX8800 Ultra Leviathan (factory watercooled)
    SLI Leadtek PX8800 Ultra
    Asus Physx card (removed)
    Dlink DWA556 PCIx Xtreme N Wireless card
    2x WD Raptor 150GB Raid 0 300GB
    1x Seagate 400GB Sata
    X-Fi Platinum Fatal1ty Champion
    24' Benq FP241VW Gamer
    Innovatek XXD Rev 2 + G-Flow water cooling
    CoolerMaster Cosmos 1000 case
    Saitek X52 Flight system
    TrackIR 4 + Trackclip Pro
    Windows Vista Home Premium 32bit
  • parkerdw - Tuesday, June 3, 2008 - link

    I used the same motherboard and cpu, but I liquid cooled it using the gigantic Kandalf Liquid Cooled case. My memory is different as well since I use 4 GB of Patriot Viper memory (2 x 2GB). Other than the memory settings in the BIOS, I set everything to match this guide. My system runs at 4.0Ghz and the cpu runs at no more than 88 degrees fahrenheit even while playing something like Crysis with everything set to Very High. Crysis runs between 35 and 60 fps on Very High on my system using a single 9800 GX2 at 1280 x 720. It's a HTPC connected to my older 56 inch DLP set via DVI, so I can't go any higher than that, but I fully expect to run great at 1080p when I get my new large screen set later this year. I don't have my bios settings in front of me, but setting everything to Auto for the memory works PERECTLY at 4.0 ghz. Pretty cool. I think it's running at 8,8,18 or so and 1.9v.

    Also, Asus just released a patch to the bios that fixes the data corruption issue mentioned in this artcle. Released on 5/29/08 I think.
  • hardist - Monday, April 21, 2008 - link

    The water block seems to have leaking issues , I am wondering why it was not covered in this review since it is a major feature of this board ......
  • Heatlesssun - Sunday, April 20, 2008 - link

    This is a sweet motherbaord! Now I've not overclocked the FSB, just bumped up the multiplier of my QX9650 from the default of 9.5 to 10, and I'm not running RAID. We shall see but I feel good. To get this up and running with Vista x64 in a day so smoothly was pretty good I thought.
  • electricx - Tuesday, April 15, 2008 - link

    So this board is going for the aforementioned amount on newegg... The EVGA and the XFX 790i boards are going for $350... The ROG name carries that much of a premium? I mean, come on?! I'm sure ASUS will fix this data corruption issue and you typically do pay more for the privilege(?) of being a beta tester for high end hardware but $1000 over competing products seems a bit much... The EVGA board is looking to be a clear winner here to me. Time will tell I suppose.
  • FightingEagle - Friday, April 18, 2008 - link

    After the second EVGA 790i and full of bugs I just sent it back. I was interested in the ASUS X48 and the 790i, but the 790i over $400 is hard to grasp. EVGA has good looking heat sink but not very good at cooling. I may wait for all the bugs to leave but as now im sitting on $320 dollars worth of DDR3 and a E8400.
  • electricx - Tuesday, April 15, 2008 - link

    Edit: That should have been $100 not $1000
  • UK1Man - Sunday, April 13, 2008 - link

    Help please!!
    I'm currently in the process of building a computer but can only afford to buy a couple of parts a month, I have already purchased some DDR2 (1066) memory for an FXF 780 motherboard (not yet purchased) but am now considering the Asus striker II extreme.
    Will my DDR 2 memory work with this?
  • seamusmc - Monday, April 14, 2008 - link

    This board/chipset, 790i, only supports DDR3.
  • ianken - Saturday, April 12, 2008 - link

    Can it go into S3 suspend and come back out and have the NICs still work? The Striker 2 Formula cannot.

    Can the SATA controller handle hot swap? The Stiker 2 Formula and the previous 680i boards could not. The 680i bios even had an esata setting that did NOTHING.

    The latest crop of Asus boards, particularly the NV chipset rigs, have been pretty buggy and basic functionality has been borked.

    But hey, who cares of the basics don't work right? it's got a water block for X-TREME OVERCLOXORS! YO! VTEC!

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