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What exactly is cpu clock skew?

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thetacowarrior
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2010/09/19 14:48:59 (permalink)
I see they added it on bios 71. What good is it? I know its an overclocking thing, but I don't know what exactly it does.

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    KenMcC
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    Re:What exactly is cpu clock skew? 2010/09/19 17:42:08 (permalink)
    Clock skew is present on PCIe buses.  It is the difference in arivial times of bits to and from each PCIe device.  I believe it also applies the DDR3 memory (in that when OCing or not) the speed of the data transfere on the parallel lines can cause some of the data to arrive so much before the reset of the data that a data error occures.   I don't know all this for sure, but the adjustment may be in pico seconds. 

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    miahallen
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    Re:What exactly is cpu clock skew? 2010/09/19 21:00:46 (permalink)
    All devices and system interconnects have to have timing to properly sync data being transferred.  When overclocking, things can get delayed or sped up at one end or the other and clock skew provides reconciliation for these slight timing changes.
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    thetacowarrior
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    Re:What exactly is cpu clock skew? 2010/09/20 08:36:51 (permalink)
    Ok thanks. From what I've read there is no really way to know which way to adjust it, its kind of a shot in the dark kinda thing, is this true?

    Or is there some sort of master's logic that I don't know about?

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    dozer3000
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    Re:What exactly is cpu clock skew? 2010/09/20 08:51:30 (permalink)
    For example, if you overclock your cpu, and the new setting work properly, then you test the system with Linx f.e., and you got an error, not a bluescreen, just an error, goto BIOS and set CPU skew to 100, ... test again, if failures again, CPU Skew 200.. 

    I've heard, that it works nice... some people have better Vcc / VTT and higher oc-results. 

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    thetacowarrior
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    Re:What exactly is cpu clock skew? 2010/09/20 20:47:49 (permalink)
    Huh, I may have to try that, I can't go past 3.6 to save my life, or at least I can but it fails LinX every time, no matter the voltage. I wonder if that may be the answer...

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    miahallen
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    Re:What exactly is cpu clock skew? 2010/09/21 02:44:33 (permalink)
    It's not going to make a big improvement.....it's simply a fine tuning adjustment.  If you're stuck at 3.6 while trying to reach 4GHz....this is not the solution....there is another problem ;)
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    thetacowarrior
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    Re:What exactly is cpu clock skew? 2010/09/21 20:16:10 (permalink)
    Yea I think I need to turn off c-states and speedstep. I was hoping to leave them both on, I understand it can be done up to about 4 ghz, but I can't seem to get it to go. I think its that because it always errors out between the linx runs, where the cpu drops down for a sec.

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