NEED HELP!

[BaLeRiON]

My pc config is:

Processor: Amd Fx8350 

Motherboard: Ga-990fxa-UD3

Ram: 4sticks of 8gbrams. Total 32gb VULCAN 1600mhz

GPU: RX 550

Windows 10

 

So my problem is that the system is showing i have 28gb of rams and only 24gb is usable. I checked all the rams on another computer and they worked perfectly.

I just want to know where and what the issue is? and if its fixable?  

 

Also i dont know why the rams are running at 1333mhz.

 

Please reply ASAP. TIA