Why does Windows Server 2012 R2 Standard edition show only 20% of my available memory?

Fellow Techies-- I have a LENOVO x3650 X6/x64 based Windows server with 4 18 cores/36 logical processors-- with installed physical memory (ram) @1.5 TB, total virtual memory @1.5 TB. However, I am showing only 295 GB of available physical memory and only 297 GB of available virtual memory. What's the story? Does the Windows Server 2012 R2 Standard edition, version 6.3.9600, build 9600 cause the limitation? I know in the 2008 windows universe of products, there was difference between the Enterprise edition and the Standard edition--but the naming convention for the 2012 server editions is different. There is a data center class of windows products for windows server 2012--is this the equivalent? Am I going down the wrong path? Should I be looking at a different explanation as to why I am only showing 20% of what I think should be available?