I have in total 4 gb + 4gb = 8 gb RAM in my machine. The problem is that, when i wanna to check the free RAM then I think there are some problem . Because you can see in the following image , total is 7.2 Gi and used is 4.2 Gi but free is only 131 Mi . But you know the free RAM should be (7.2-4.2)=3 Gi. Please tell me anyone what actually the problem .