HX850 - CPU voltage in BIOS constantly changing between 1.136V and 1.144V - Normal?

[lalittle]

I have two identical systems using HX850s. On one of them the "CPU Voltage" reported in the BIOS is completely stable at 1.136V. On the other, however, the BIOS shows the CPU voltage continually bouncing up and down between 1.136V and 1.144V. I realize that this is only a 0.7% difference (0.008 volts), but I'm used to seeing completely stable CPU voltages in the BIOS, and I can't seem to find any information on how much fluctuation is normal for this particular voltage. Since the other system isn't doing this I just want to confirm whether or not this is normal.

 

Note that this is when simply monitoring the voltages/fan speeds on the "Hardware Monitor" page of the BIOS (Asus P6X58D Premium, i7 950.)

 

Thanks,

 

Larry

[lalittle]

I see various specs for acceptable margins of error for the 3.3, 5, and 12 volt rails, but I can't find this information for the CPU voltage. Is this even something that the power supply effects, or is this entirely regulated by the motherboard?

 

Thanks again,

 

Larry

[trackrat]

Intel's voltage tolerance for ATX PSUs is +/-5% for the 3.3V, 5V and 12V positive voltage rails. See table 6, section 4.1.4. Typically you will see tighter regulation of 3% on the 3.3V and 5V rails on better PSUs however. The CPU voltage is regulated by the mobo circuitry, not the PSU.

 

Note that BIOS voltage readouts are rarely accurate. You need a quality digital volt meter or scope to accurately measure PC mobo voltages. I've seen the actual CPU voltage circuit on the mobo vary considerable from one mobo to another depending on the quality of the circuitry and components.

 

http://www.formfactors.org/developer%5Cspecs%5Catx2_2.pdf

[lalittle]

Forgive me, but this doesn't address the cpu voltage, which is what I'm asking about. That document doesn't talk about the cpu voltage at all as far as I can tell.

 

Note that I'm not just asking about overall voltage numbers/tolerances. I'm asking if it's normal for the voltage to fluctuate in the BIOS like I described, and if the PSU has any bearing on the CPU voltage, or if this is completely controlled by the motherboard.

 

Once again, the thing that bothers me a bit is that an identical system does not do this at all.

 

Thanks again,

 

Larry

[Yellowbeard]

I have two identical systems using HX850s. On one of them the "CPU Voltage" reported in the BIOS is completely stable at 1.136V. On the other, however, the BIOS shows the CPU voltage continually bouncing up and down between 1.136V and 1.144V. I realize that this is only a 0.7% difference (0.008 volts), but I'm used to seeing completely stable CPU voltages in the BIOS, and I can't seem to find any information on how much fluctuation is normal for this particular voltage. Since the other system isn't doing this I just want to confirm whether or not this is normal.

 

Note that this is when simply monitoring the voltages/fan speeds on the "Hardware Monitor" page of the BIOS (Asus P6X58D Premium, i7 950.)

 

Thanks,

 

Larry

Sounds like the power management functions of the CPU to me. Are all the settings in the BIOS for EIST/C1E, etc exactly the same?

[trackrat]

Forgive me, but this doesn't address the cpu voltage, which is what I'm asking about. That document doesn't talk about the cpu voltage at all as far as I can tell.

 

Note that I'm not just asking about overall voltage numbers/tolerances. I'm asking if it's normal for the voltage to fluctuate in the BIOS like I described, and if the PSU has any bearing on the CPU voltage, or if this is completely controlled by the motherboard.

 

Once again, the thing that bothers me a bit is that an identical system does not do this at all.

 

Thanks again,

 

Larry

 

You evidently missed my comments that the PSU does NOT control the CPU voltages, that you need to use a DVM or scope to measure the mobo voltages and that I have seen considerable variation in mobo CPU circuit voltages based on the component quality and circuit design... ;):

[lalittle]

Sounds like the power management functions of the CPU to me. Are all the settings in the BIOS for EIST/C1E, etc exactly the same?

 

Yes -- all settings are exactly the same, which is to say that everything is at the BIOS "setup defaults."

 

You evidently missed my comments that the PSU does NOT control the CPU voltages, that you need to use a DVM or scope to measure the mobo voltages and that I have seen considerable variation in mobo CPU circuit voltages based on the component quality and circuit design... ;):

 

You're right -- I'm not sure how I missed that.

 

So the bottom line question is this: Given that one system does this and the other does not, is there any reason to worry about it, or is this too small of a fluctuation to be concerned with? You said that there "can be" considerable variation, but if only one system does NOT do this, does that indicate that the components and design of this motherboard "should" be preventing this from happening at all?

 

In other words, does the fluctuation point to a potential issue with the quality of one motherboard vs the other? I just don't have any point of reference for whether this is even "possibly" an issue. I wanted to check this before I got further into the build and OS install.

 

I'm also not sure what "considerable variation" might be. Would I be correct in assumng that 1.136 to 1.144 would be considered "extremely minor" variation?

 

Thanks again,

 

Larry

[trackrat]

Yes the diff between 1.136 and 1.144 is an extremely minor variation and not likely any issue at all.