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Corsair XMP increasing CPU temps

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July 12, 2012 12:36:43 AM

Hey folks,

I bought some new RAM, replacing my old 4 gigs of G. Skill to 8 GB Corsair Vengeance (4x2) 1600 mhz. CMZ8GX3M2A1600C9B

Upon install, I opened up BIOS. The memory was clocked at 1333 mhz. The RAM was auto clocked, so that's cool. I changed memory profile to "profile 1," saved, quit, went to the desktop.

Normally my CPU temps when internet browsing/idling are about 33-37 degrees C. Pretty normal. With the new RAM and XMP in place, my CPU temps on idle were up to 45-50 degrees C. Again, safe, but much too high for idling.

Is that normal? I've never tried xmp before, but that seems kinda ridiculous.
I went back into BIOS and put the RAM back to auto clock (1333mhz) and surely enough CPU temps once back at desktop were down to their regular mid 30's.

What's going on here?

Thanks for the help!


EDIT: my MOBO: Gigabyte GA-P55A-UD3
processor: intel i7 860 @ 2.80 ghz (stock speeds)

UPDATE: I played various games (WoW, D3, BC2) and none pushed my processor to dangerous levels (max 64 degrees C). It just idles really warm...
July 12, 2012 5:31:37 AM

i found this link: http://www.tomshardware.com/forum/269314-30-drastically...

apparently it's the motherboard?

EDIT: so i read through the link here, and per suggestion found that the idling CPU core voltage was higher with XMP active (roughly .88V without XMP and 1.14 with). It is likely that this is leading to the higher temps.


EDIT 2: so I tried upping the RAM frequency from 1333mhz to 1600 mhz manually. and wouldn't you know it, the CPU core voltage went back up to 1.136.

Must the CPU voltage go up with RAM frequency? this seems odd.


EDIT 3: Also interesting. My CPU is set to down step when idling, as set in the bios. That DOES NOT HAPPEN with the RAM frequency is 1600 mhz. At 1333mhz, I noticed that the CPU core voltages would fluctuate a little bit, but when idling, it would turn down a bit, which would make sense cause the CPU would be downstepping. There is 0 downstepping going on while the RAM is at 1600 mhz. In fact, according to CPUID, the current, min, and max, CPU core voltages are 1.136, meaning that my CPU is not downclocking at all. Most interesting indeed.


In summary: So after my detective work, I figured out that the heat difference while idling was caused by differences in CPU core voltages while idling. The differences in idling voltages are related to the CPU idling clock speed. For whatever reason, with the Gigabyte P55-UD3 board, when the RAM is clocked from 1333mhz (auto) to 1600 mhz, either by XMP or manual RAM clock increase, the CPU does not downstep while idling. It stays at 2.8Ghz, or a 21 multiplier. Conversely, when the RAM is at 1333Mhz, the CPU generally downsteps to x9 multiplier (1.2GHz) while idle. Thus, in turn, lowering the Core voltage and with it, the CPU temperatures. A solution? If you need to run your RAM at 1600mhz, I'd suggest getting a program to manually control CPU clock speed and downclock when you're idling.
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July 12, 2012 11:46:43 AM

Hmm, I have a feeling it's from the profile selection, though. If you try resetting the BIOS and manually OC the RAM do you get the same problem?
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July 12, 2012 1:57:13 PM

yes, upping the RAM to 1600 using XMP or manual OC prevents the CPU from downstepping, therefore keeping the higher voltage level and temps while idling. apparently, it's this particular motherboard that does this. other people have been having the same issue.
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