Windows 10: can someone explain why there is 15.9 usable ram after i changed my motherboard?

can someone explain to me why there is 15.9 usable ram after i changed my motherboard?

:)

 

usable RAM

Hi,

There are several reasons why this is happening. It could be an issue with hardware, configuration in BIOS settings and computer architecture as well. To help you with this, we need more information about your machine. Please answer the questions below:

• Which version of Windows you are using? Please follow the steps on this
  link on how to check it. Also check if you have 32 or 64 bit operating system installed.
  
• Have you made any changes to your machine before this issue occurs?

For the meantime, please follow the steps on this link on how you can maximize
the usage of your memory.

If you are using custom build computer, it would be best to check if the hardware is compatible to your motherboard.

We'll be waiting for your response.

 

installed RAM 16 (7.9 usable)

My upgrade from my old graphic card to the new one gives me this headache. Please someone help me. I tried every thing my motherboard is cleaned and my ram all 4 working but only 2 slot read and use #(1-2) no matter which 2 from the 4 rams they work but the other 2 slot never(3-4) I'm the motherboard can be usable. please help

My pc spec:
Moutherboard: asus m5a99fx pro r2.0
CPU: AMD fx-8350 4.00 GHz
GPU: EVGA GTX 1070 ti SC
RAM: kingston hyperx beast ddr3 4G x 4 Pieces
System type: windows 10 pro 64 bit
Power supply: 600 wat gamemax

screen shot attached
help pleasssse *cry

 

Windows 10 usable ram

Hi,

Most applications and hardware components require a reserved memory allocation during the boot up process of your computer. Now it is possible to change those settings in your computer or inside the BIOS settings to maximized the total available RAM you
have in your computer. Before we proceed with the next steps to resolve your concern, kindly provide the answers to the questions below:

• Which version and build of Windows 10 do you have installed in your computer?
• Since you mentioned about changing the BIOS settings, have you checked with your motherboards manufacturer's website if there is an update available for your BIOS?
• What troubleshooting steps have you completed?

We look forward to your response to our queries.