Hi Julian,
I am Dave, I will help you with this.
This is normal if your PC has integrated graphics, that will cause Windows to set aside maybe 1/4 of your RAM for your graphics, because integrated graphics does not have any VRAM and uses shared System RAM.
Open Task Manager (Ctrl + Shift + Esc)
Select the Performance tan in Task Manager and click Memory on the left
Please provide a screenshot of that Task Manager window.