16gb ram only showing 8gb usable, but 16gb installed windows 10 (whatever win 7 ultimate upgraded to)

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Jun 19, 2015
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so basically I bought a second set of corsair vengeance black 4gb sticks, (I had 8gb orginally) upon installing them I found to my surprise windows has recognized there is 16gb installed, however there's only 8gb "usable" I've tried the "advanced boot settings" method and i couldn't get it to use all 16gb, any ideas here? (4x4gb stick layout)
 

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Jun 19, 2015
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mobo : msi gaming 970
cpu : amd fx 8320
dram model is : cmz8gx3m2a1600c9 (I think)
there's only 4 slots, and there's a stick in each slot, like I said I had 8gb before, added the other 8 today, they should be the same ram from what I've looked at. that being said the first pair (orginal pair) are on the far right slots, and the 2nd pair (new) are on far left, and windows is recognizing it as 16gb installed, but only showing 8 is usable, I'm 99% sure these are dual channel, but the other set was too, so theoretically they should be completely usable right?
 

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Jun 19, 2015
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So, after booting into bios to confirm the orginal dram was the same model, I figured it out, it wasn't the dram voltage itself, but the dram clock, it was set the default, so I bumped it up to 1600mhz (because that's the advertised frequency for the modules) saved and booted back into windows and it worked! 16gb fully usable, thanks for the help :)
 

zuhair mohammed

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Sep 4, 2016
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hi,I have problem ,I got 4x4 ,G.SKILL Ripjaws X Series 4GB 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800) Desktop ,fireston memory card ,windows 10 home 64 bit is recognizing it as 16gb installed, but only showing 8 is usable, I know it's in the Bios,but I don't know how to fix it.
msi-(Ms-7588)
i7 CPU 880 @ 3.07 GHz
graphic card nvidia/Geforce GTX 750 Ti