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14GB RAM installed but only 7.98GB usable Windows 7 64-bit

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January 10, 2014 8:15:57 AM

I am using a new Gigabyte GA-990FXA-UD3 motherboard with an AMD Phenom II x4 965 cpu. I originally only had a single 8GB stick of DDR3 1600Mhz which worked fine, but to upgrade that I only had 4x2GB DDR3 1600Mhz sticks. So the current setup starting at the slot closest to the cpu is 8gb, 2gb, 2gb, 2gb. The only thing I can think of that is causing this is the dual-channel mode failing to utilize the extra space because of the difference in capacity of the sticks. I don't know if it makes a difference but I am using a 64GB SSD as the root drive that only has 12GB available space which limits the paging file size for virtual ram. I have tried re-seating the RAM, taking the CMOS battery out, checking for BIOS updates/RAM settings, and checking msconfig boot to make sure It wasn't limiting anything. Any help on this issue would be greatly appreciated.
January 10, 2014 8:27:00 AM

i would assume its juts not supported by your mobo, mixing different kinds of ram capacity sticks together is always a source for problems as far as ive heard, and i would definetly suggest using dual channel on the same capacity stick for compatability reasons
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January 10, 2014 2:12:56 PM

The 990FX chipset uses a dual channel memory controller, which means the memory needs to be installed in pairs. The way you did things makes the chipset read all 14GB of memory, but it will only be able to use 2GB from that 8GB DIMM because it is paired with a 2GB DIMM. Only install memory in pairs, as designated in the manual.
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January 10, 2014 11:52:18 PM

dguinnea32 said:
I am using a new Gigabyte GA-990FXA-UD3 motherboard with an AMD Phenom II x4 965 cpu. I originally only had a single 8GB stick of DDR3 1600Mhz which worked fine, but to upgrade that I only had 4x2GB DDR3 1600Mhz sticks. So the current setup starting at the slot closest to the cpu is 8gb, 2gb, 2gb, 2gb. The only thing I can think of that is causing this is the dual-channel mode failing to utilize the extra space because of the difference in capacity of the sticks. I don't know if it makes a difference but I am using a 64GB SSD as the root drive that only has 12GB available space which limits the paging file size for virtual ram. I have tried re-seating the RAM, taking the CMOS battery out, checking for BIOS updates/RAM settings, and checking msconfig boot to make sure It wasn't limiting anything. Any help on this issue would be greatly appreciated.


What edition of Windows 7 are you running? Windows 7 Home Basic x64 is limited to 8GiB of physical memory.
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January 11, 2014 4:37:46 AM


It's Windows 7 Pro
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January 11, 2014 5:56:08 AM

dgingeri said:
The 990FX chipset uses a dual channel memory controller, which means the memory needs to be installed in pairs. The way you did things makes the chipset read all 14GB of memory, but it will only be able to use 2GB from that 8GB DIMM because it is paired with a 2GB DIMM. Only install memory in pairs, as designated in the manual.


Thank you, I was afraid this was the issue. After replacing the three 2gb sticks with another 8gb, my system is able to recognize all 16gb of RAM. Luckily I was able to find someone on craigslist willing to trade 4x2gb sticks for a single 8gb :) 
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January 11, 2014 6:16:27 AM

dguinnea32 said:
dgingeri said:
The 990FX chipset uses a dual channel memory controller, which means the memory needs to be installed in pairs. The way you did things makes the chipset read all 14GB of memory, but it will only be able to use 2GB from that 8GB DIMM because it is paired with a 2GB DIMM. Only install memory in pairs, as designated in the manual.


Thank you, I was afraid this was the issue. After replacing the three 2gb sticks with another 8gb, my system is able to recognize all 16gb of RAM. Luckily I was able to find someone on craigslist willing to trade 4x2gb sticks for a single 8gb :) 


I'm glad to hear you found a good solution, with even more memory than you expected, too.

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April 24, 2014 9:07:24 PM

Well, I have two 8gb memory sticks (gskill make, same model) on my system which has windows 7 home basic 64 bit and motherboard is Asus Gryphon Z87 which supposed to support 32 GB memory.

But my system shows only 16 GB total memory and 8 GB usable memory. Can anyone help?

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a c 1504 V Motherboard
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April 24, 2014 9:55:46 PM

That one is fairly easy, Win 7 Home basic only supports 8GB total DRAM, sorry to be bearer of bad news, Home Premium supports up to 16 GB
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