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Thread: CPU PLL effect on overclocking




  1. #1
    boondocks's Avatar
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    Default CPU PLL effect on overclocking

    At mild overclock (4.5GHz) I went into the BIOS before any testing and got the red screen warning about overclock problems. So, after booting up after the red screen I ran Intel Burn Test for a quick look and it failed.
    After a ton of reading and looking at voltages I lowered the PLL slightly from the 1.8V nominal and then was able to pass IBT. (no further testing yet as I had some torrents to seed).

    From what I understand CPU PLL is one of those mysterious things that no one short of an EE degree knows much about, either raising or lowering might produce a stable clock.
    Does that pretty well sum it up, so is my adjustment smoke and mirrors or a valid step?
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  2. #2
    Chike is offline Senior Member
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    Default Re: CPU PLL effect on overclocking

    Does that make it different from other voltages?
    What does anyone know about Vcore, Vccio, Vccsa, or even DRAM Voltage other than more or less of any of them may help stabilization?

    You can't argue with success providing that your CPU does run at the clock you set it to and you don't get the red overclocking warning anymore. To be sure you can set it back to it's default and see if IBT fails amd/or the warning apears again.

  3. #3
    Lsdmeasap's Avatar
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    Default Re: CPU PLL effect on overclocking

    Are you wanting some information on CPU PLL, or are you just asking if it's normal that lower can help?

    Haha, yes, it's normal that lower can help! I often suggest this to users, especially on newer boards as it's generally set too high by auto these days.

    If you want info about what CPU PLL does, let me know and I can link you to some information about it.

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    Default Re: CPU PLL effect on overclocking

    Quote Originally Posted by Chike View Post
    Does that make it different from other voltages?
    What does anyone know about Vcore, Vccio, Vccsa, or even DRAM Voltage other than more or less of any of them may help stabilization?

    You can't argue with success providing that your CPU does run at the clock you set it to and you don't get the red overclocking warning anymore. To be sure you can set it back to it's default and see if IBT fails amd/or the warning apears again.
    Ah, I don't know. Literally.
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    Default Re: CPU PLL effect on overclocking

    Quote Originally Posted by Lsdmeasap View Post
    Are you wanting some information on CPU PLL, or are you just asking if it's normal that lower can help?

    Haha, yes, it's normal that lower can help! I often suggest this to users, especially on newer boards as it's generally set too high by auto these days.

    If you want info about what CPU PLL does, let me know and I can link you to some information about it.
    No, I don't need any specific info other than verification that this is a normal tweak, as I said I couldn't find much info about it. I had read a bunch of old posts here and there where people were talking about radically increasing that voltage, and a few probably more relevant to Sandy Bridge that suggested the adjustment may go either way, up or down.
    I'm not especially paranoid about blowing anything up, I just have a lot to learn.
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    Default Re: CPU PLL effect on overclocking

    OK, yes it's completely normal!

    Increasing CPU PLL was only necessary in older boards like P45 or earlier, since X58 and above it's not really needed, nor does it often help to raise it, actually the opposite as stock seems to be a bit high usually.

    P45 or below = raise helps stability and increase could help increase OC

    X58 and above = lower to start, stock is often too high, going above stock value rarely helps at all, does not tend to affect OC at all unless it's too high and then it brings instability.

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    Default Re: CPU PLL effect on overclocking

    Quote Originally Posted by Lsdmeasap View Post
    OK, yes it's completely normal!

    Increasing CPU PLL was only necessary in older boards like P45 or earlier, since X58 and above it's not really needed, nor does it often help to raise it, actually the opposite as stock seems to be a bit high usually.

    P45 or below = raise helps stability and increase could help increase OC

    X58 and above = lower to start, stock is often too high, going above stock value rarely helps at all, does not tend to affect OC at all unless it's too high and then it brings instability.
    Thanks! Sorry about slow replies-been pretty busy around here.
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    Default Re: CPU PLL effect on overclocking

    I have been checking email, but not getting any notifications on threads like I usually do. Checked the general settings, instant notification by email is set, so I re-saved it and maybe it will work again.
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  9. #9
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    Default Re: CPU PLL effect on overclocking

    No worries about slow replies, we all have real lives and are often busy, so we're never expect instant replies anyway so you're all good!

    Yes, sorry about that, email notifications are disable right now. I reminded Mr.Tweak to turn them back on last night, hopefully he'll see that email soon and enable them again

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    Default Re: CPU PLL effect on overclocking

    I just wanted to confirm that lowering the CPU PLL voltage on my GA-Z68XP-UD4 (revision 1.3) board definitely helped improved stability. Specifically passing 12 hours of Prime95. For the world of me I couldn't pass 12 hours of Prime with CPU PLL voltage set at auto or manually setting it to 1.80v

    After reading a lot of overclocking related posts on the Gigabyte Z68 boards I decided to start playing with the CPU PLL voltage. I started at 1.70v and slowly worked forwards and backwards from there. I seem to have found a sweet spot at 1.76v set in BIOS. Now I'm solid as a rock in all apps, games and can even pass 12 hours of Prime95 :)

    I also noticed on BIOS F6 that VCCSA is auto set slightly below the Intel "recommended" value. Mine auto set at .920v - Intel says .925 so that is where I manually set mine.

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    Last edited by wevsspot63; 03-20-2012 at 09:52 PM.

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