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So I have 16GB RAM. After upgrading to Windows 10 however it says I only have 8GB. When I look in task manager it seems to know I have 16GB but for some reason only using 8Gb of it and for slots used it says 2 of 4 when I'm using all 4 RAM slots.

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I am assuming it means the CPU can only use 2 ram sticks at the same time, but would that mean installing 4 sticks of 4gb ram will only be used to the extent of 2x 4gb ram?