RStudio Desktop with Windows Server 2016 and Memory Restrictions

Hi all,
I've started using RStudio Desktop with Windows Server 2016 hoping to take advantage of the power of both. However, I faced the problem limitation of memory restriction on R by Windows Server. So, for instance, applying the memory.size(size=65000) doesn't imply that I can use all the available memory rather I can use only 10% of that size when I run complex analysis on big data size.
I'm not sure if I'm right in my analysis of the problem or if you are facing the same problem and I don't know how to solve the problem. I didn't use RStudio server.