Using more of that memory installed in your server.
The following are the memory limits for the various versions of Windows Server 2003 R2
Version Limit X86 Limit X64
Windows Server 2003 R2 Datacenter Edition 64 GB (16 GB with 4GT) 1 TB
Windows Server 2003 R2 Enterprise Edition 64 GB (16 GB with 4GT) 1 TB
Windows Server 2003 R2 Standard Edition 4 GB 32 GB
But these limit which are over 4GB for the 32-bit versions assume the use of Physical Address Extension (PAE)
To enable PAE, use the /PAE switch in the Boot.ini file.
The following is an example of a Boot.ini file where the PAE switch has been added:
[boot loader]
timeout=30
default=multi(0)disk(0)rdisk(0)partition(2)\WINDOWS
[operating systems]
multi(0)disk(0)rdisk(0)partition(2)\WINDOWS="Windows Server 2003, Enterprise" /fastdetect /PAE
Edit the Boot.ini file
To view and edit the Boot.ini file, follow these steps:
1) Click Start, point to Settings, and then click Control Panel.
2) In Control Panel, double-click System.
3) Click the Advanced tab, and then click Settings under Startup and Recovery.
4) Under System startup, click Edit.
Details in links below:
https://msdn.microsoft.com/en-us/library/windows/desktop/aa366778%28v=vs.85%29.aspx#physical_memory_limits_windows_server_2003_r2
https://support.microsoft.com/en-us/kb/283037
https://support.microsoft.com/en-us/kb/317526