Usable ram ?

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I recently upgraded from windows 8.1 64bit to windows 10 pro 64bit through the upgrade system and then once updated my ram was now spilt 8gb shown in bios and in cupz but only in single channel and is show in system info as 8gb installed (3.95gb usable) so would a fresh install of windows as i have already reseated the ram changed slots ect and i have also reseated the cpu. i have also checked the maximum memory in msconfig.

Thanks in advance 

 

System specs 

FX 8320 

Ripjaws Gskill 

MSI 970 Gaming Motherboard

Msi 980 Gaming 

 

I have also just looked at task manger and it says that there is 4.1gb reserved for Hardware.

[Naeaes]

The RAM could be incompatible? Here's the compatibility tool for G.Skill and here's the tested RAM list for MSI-970-Gaming.

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Corsair CMY16GX3M2A1866C9R Vengeance Pro Series 16GB (2x8GB) DDR3 1866Mhz CL9 XMP Performance Desktop Memory Kit Red are these okay ? Thanks

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installed the ram today and it now says 16gb (7.95 GB usable)