Dell Optiplex 990 12GB memory installed 3Gb usable

I just upgraded the memory for this system. It says 12GB installed (3.17GB usable). In the bios it says 12288MB installed 12176MB available. Any ideas? Maximum memory is not checked in advanced startup. windows 8.1 operating system.
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Is it a 64 bit OS?
JohnBusiness Consultant (Owner)Commented:
The most obvious reason why this would happen is that you have a 32-bit operating system and 3 GB is the 32-bit limit.

Is this correct?

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You can check this in the Control Panel in the System section.    It will tell you in the "System"/"System Type" section.
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CubbybulinAuthor Commented:
yeah silly me, i realized it in the meantime and installed 64 bit and all ok. thanks!
noxchoGlobal Support CoordinatorCommented:
You have 32bit Windows version and the RAM which exceeds the size of 4GB is useless for you.
You cannot upgrade or update the OS to 64bit which will use entire amount of your 12GB RAM. You need to install from scratch the 64bit Windows.
Are you using Non-ECC dual-channel 1333MHz DDR3 SDRAM?  And if you are, did you make sure it is properly set in the slots?
JohnBusiness Consultant (Owner)Commented:
Thanks, and I was happy to help.
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