Breaking the Overclock Lock

Both Abit and Asus employ similar methods to work around the Overclock lock, with varying degrees of success. Both manufacturers looked at chipset voltage, but decided it only provided limited enhancement for 925X/915 overclocking. They both provide this option in BIOS, but it is not a major part of the Overclock workaround.

At boot, both Asus and Abit manipulate the PCI Express frequency and set ratios that result in a lower PCIe frequency than would be expected at a given clock frequency. Since PCIe frequency and CPU clock frequency are derived from the same PLL, then a Clock frequency of 258 (FSB of 1032), for example, would result in a PCIe frequency of 129. In fact, the Abit PCIe clock at 258 is 118, below the maximum of 120 for most nVidia PCIe cards.

Abit officially explained this as:
"ABIT found something to do with uGuru technology to improve the OC behavior after BIOS v1.1was released. Now, uGuru hardware will auto sense the CPU external clock and figure out a stable PCI-E clock, and then uGuru tells BIOS v1.3 beta to run the calculated and optimized PCI-E clock. It's the reason why BIOS v1.3 beta is better for OC than v1.1. Why does the system hang when changing PCI-E clock in uGuru software in 1.3? Because the PCI-E clock is calculated and most stable in special OC conditions; changing it will induce system instability."
Abit's solution appears to stop there, as we found that SATA still fails at about 260 Clock Frequency. This is why you have seen others reporting higher overclocks on the Abit board with IDE hard drives combined with PCI video or ATI PCIe.

Asus, in addition to manipulating the PCIe frequency at boot, also manipulates the link frequency between the North and South bridge on the chipset to limit the "trigger" frequency for SATA failure. This allows the Asus P5AD2 to break through 258 and reach the highest overclock that we have yet seen of 278 with a normally equipped 775 system with both an ATI PCI Express video card and a SATA Hard Drive. This appears to be the limit of our 3.6ES CPU at a 14X multiplier, and Asus believes even higher overclocks are possible with later and better overclocking Socket T Prescotts.

Engineers at both Asus and Abit tell us that they do not believe it is possible to implement a true PCI Express lock on the 925X/915 chipsets, while still achieving overclocks that will satisfy enthusiasts. The best that they believe can be done to remove the PCIe, Link Frequency, and SATA failure from 925X/915 overclocking is to manipulate the boot algorithms for PCIe frequency and link frequency. Slightly higher overclocks are also possible using increased voltage to the chipset, but this still does not fix the PCIe and SATA issues. Onboard graphics in the 915G chipset are also reported to overclock much higher, since the graphics are on-chip and not influenced by the PCIe frequency and link frequency in the same manner.

ATI, nVidia and the PCI Express Limits

There has been no difference at all in the performance results in our comparison of nVidia's bridged solution for PCIe and ATI's native PCIe video cards. However, we have run into our first difference with the two PCIe solutions on an overclocked 925x platform. The nVidia bridged PCIe solution is stable to about 250 to 258 CPU clock on the Abit and Asus 925x motherboards and then it fails at any higher FSB. The ATI PCIe cards, on the other hand, continue on to our CPU limit of 278.

We know for a fact that ATI's PCIe is more tolerant of out-of-spec PCIe frequencies in our tests, but we do not know why this is the case. The Engineers we talked with speculated that ATI's native PCIe solution had less overhead than the bridged nVidia PCIe and therefore handled higher PCIe frequencies. We cannot confirm this as an explanation for what we observed. We only know that the nVidia PCIe we tested - 6800 Ultra, 6800 GT, and NV45 - all topped out in the 250 to 258 range. The ATI PCIe that we tested - X600 and X800XT - all reached the top test frequency of 278 on the Asus board. Keep in mind that we could not verify this on the Abit board, since SATA failed at about the same frequency as nVidia PCIe. However, others have reported reaching higher overclocks on the Abit board as well with the combination of ATI PCIe and an IDE hard drive.

Does This Also Work on the 915 chipset?

Asus tells us that the techniques, which they have used on the P5AD2, are even more effective on their 915 chipset motherboards. Asus Engineers say that the enhanced memory performance unique to the Intel 925X chipset makes it more difficult to manipulate the PCIe frequency and link frequency at boot. It is simpler to control these frequencies on the 915 chipset. As a result, Asus has been able to reach a bit higher overclocks on their 915 boards using these techniques.

Engineers have reached 290 on a 915 chipset board using the same components that topped out at 283 on the 925X. They believe this is the CPU limit and later processors with more overhead will reach even higher. The real difference in overclocking abilities between the 915 and 925X appears small, and the message here is that manufacturers like Asus can provide the same overclocking capabilities on the 915 that are available on the 925X.

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  • jiulemoigt - Saturday, July 24, 2004 - link

    I did have to laugh at #5 "Because of DDRII and the hugely overclockable Prescotts, the potential for massive Intel overclocks without extreme cooling and wads of cash would be huge." I remember the last space heater we were told would be a great thing, I think it ended up with a vacum cleaner nickname... DRII will not be faster than DRRI until they get it to the point DDRI is at now. and prescot is the reason intel requires mobo marker to design the mobo with a bolt on heatsink design... Intel survives on marketing along at this point. Reply
  • gimper48 - Wednesday, July 21, 2004 - link

    Wes, Thanks for the response man. Yeah I see what you mean. I didn't take it the same as you I was interpreting it differently. I do not see it as an argument only as a need for more testing.. Peace, Reply
  • Wesley Fink - Tuesday, July 20, 2004 - link

    #12 & #13 - I am not going to get into an argument with HardOCP, but I stand by what is posted here. I have read the [H] article and there is absolutely nothing in the article which proves otherwise to anything posted here.

    All of the testing here was with a 520W 24-pin Power Supply as already stated in the article. We found the 24-pin high-power solution with 6800 Ultra long ago - it is not a new revelation. We also reached 258-260 with the 6800 Ultra and 278 with the ATI X800XT.

    The highest result shown at [H] was 255 with either card, so the results there were not even in the same ballpark. In fact they didn't even reach the limit we found with the Abit AV8, let alone enter the new territory from 260 to 278 that is available with the Asus.
  • gimper48 - Tuesday, July 20, 2004 - link

    I forgot to include the article that the comments are refering to Reply
  • gimper48 - Tuesday, July 20, 2004 - link

    This is what one of the reviewers at had to say about this article and from what I read it seems true. More testing is definitely needed.

    Originally Posted by gimper48

    This gives some interesting insite to the overclock lock.

    And there are some things in there as well that I think are just wrong. I think his #2 statement is incorrect and so is #3. I have proven different here on our test equipment. We are OCing far beyond his 10% with no tweaks at all with a retail CPU. We saw the same issues with the engineering sample CPU.

    The SATA does have a lot to do with it though. And I do agree with his statement that ATI seems to be more tolerant, at least on the newer VPUs.

    It looks as though one thing is for sure, solid OC boards from "everyone" is not going to happen on the 925/915 front. With the latest Asus BIOS, our OCs actually got worse not better. There is still a lot of half-truths everywhere on this. That is one reason we did not get into theorizing explanations that we were not sure of backed up with limited test data using just engineering sample CPUs.
  • gamara - Monday, July 19, 2004 - link

  • dvinnen - Monday, July 19, 2004 - link

    #6 The reason for the multiplier lock was not to limit overclocking, but because some people were abusing it. They would set the multiplier of a 2000+ (or any proc) higher and sell them as a higher rated processor. There was a lot of these conterfit processors floating around last year so they had to lock it. Reply
  • tfranzese - Monday, July 19, 2004 - link

    I was already planning on an AMD64 system once PCI-E comes out w/nForce 4 chips. This just solidifies that decision at least till the fall/winter. Reply
  • mindless1 - Monday, July 19, 2004 - link

    "goodbye until you clean up your act"

    It'll happen alright, for each and every customer who shuns intel because of this... including me.
  • MadAd - Saturday, July 17, 2004 - link

    #1. "goodbye until you clean up your act"? Nah its just not going to happen. The best we can hope for is that the Intel enthusiast crowd only buy the Abit/Asus unlocked boards and put a sour taste in the finances of other mobo manufacturers that did stick to the reference design.

    Lower sales of boards, lower growth, less willingness to develop/support every sub version, less willingness to licence from intel at all yadda ya .... however if the market share of enthusiasts is as small as some make it out to be then we dont really have a choice and intel wouldn't even notice if we did say "goodbye until you clean up your act"

    Even tho some see Intel as the evil leader and AMD the underdog, I find it uncomfortable having no choice in a market of anything, even an AMD only choice.

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