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G.Skill 2x4gb 1866 MHz issue - won't go above about half the clock I set

post #1 of 5
Thread Starter 
Before I start, here is my rig:

Phenom II 1090t @ 3.72 GHz (cooled by a Corsair H50 closed circuit water cooler)
2x 6870 1gb in crossfire
Asus Crosshair IV formula mobo
800w Cooler Master PSU
120gb Mercury Electra 6G SSD
Some old 750gb hard drive

And, the part in question, the 2x4gb 1866 MHz G.Skill ram.

For some reason, although I have the ram set to 1856 MHz in the BIOS, it will not exceed 911 MHz. This low clock is reported by CPU-Z, AMD Overdrive, and CPUID Hardware monitor. This is after fiddling with the settings beforehad, when I noticed that my memory clock was only 800 MHz, with the BIOS setting being 1600.

I am not sure why the actual clock of the ram is more than halved. It does not go up while under load, although I have been told that that is normal. My question is, why is this happening, and what can I do to fix it?

Any assistance would be much appreciated.
post #2 of 5
The speeds you're seeing in those programs are right. If you have 1600 set in the BIOS, CPU-z will show 800. It's totally normal. However, I'm not sure why your memory won't run 1866 (which would show as 933 in CPU-z).
magg0rt
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magg0rt
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post #3 of 5
Thread Starter 
So, the memory actually is performing to spec? That's so odd. I never would have expected that.

Thanks for the help.
post #4 of 5
Quote:
Originally Posted by Homicidalbarber View Post

So, the memory actually is performing to spec? That's so odd. I never would have expected that.
Thanks for the help.
Indeed. I believe it has something to do with the naming scheme/how memory works. DDR = double data rate, so if the memory is running at 800mhz, its "effective" speed is 1600.
magg0rt
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magg0rt
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32GB Samsung 30nm RAM (8x4GB) 240GB Seagate SSD (Windows 8.1) 120GB Samsung 840 Pro (Fedora Linux) 120GB PNY XLR8 SSD (Steam) 
Optical DriveCoolingOSMonitor
HP DVD Writer 1070r Corsair H100i Windows 8.1 Pro x64 Planar SA2311W (120HZ) 
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post #5 of 5
Double Data Rate RAM, aka "DDR" processes TWO bits of data for each clock cycle so the true frequency is 1/2 the advertised frequency.

http://en.wikipedia.org/wiki/DDR_SDRAM

It's worth noting that high speed rated RAM is NOT guaranteed to run beyond the default RAM speed for your CPU. In the case of an AMD Phenom II CPU the default RAM frequency is 1333 MHz. The RAM may be certified of being "capable" of running at higher speeds than the CPU will allow it to as the two components must work together reliably and the CPUs are not rated to run the RAM at the higher frequencies that the RAM is capable of.

It is fairly common however for Deneb CPUs to run DDR3 RAM at up to ~1600 MHz. without issue. Thuban CPUs typical run RAM at ~1800 MHz. reliably. FX CPUs tend to run RAM at 2000+ MHz.

http://www.overclock.net/t/1264141/memory-gskill-tridentx-2400-mhz-at-crosshair-v-formula-and-fx-8150
Edited by AMD4ME - 6/21/12 at 6:49am
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