windows - Task manager shows only 50% of RAM usage

I've 8GB RAM, but the task mangers shows me processes % of 4GB only.

i.e. Google Chrome uses 457MB and the task manger show that is 11.3% of RAM and that means 100% is about 4GB??

task manager usage

I'm using windows 10 and these are
some of my specs info

I checked the Resource Monitor and it shows me that there are 3221 MB cached? Is that normal? and how to fix it?
Resource Monitor & RamMap