In modern operating systems, including Windows, application programs and many system processes always reference memory using virtual memory addresses which are automatically translated to real (RAM) addresses by the hardware. Only core parts of the operating system kernel bypass this address translation and use real memory addresses directly. Virtual Memory is always in use, even when the memory required by all running processes does not exceed the amount of RAM installed on the system. An expanded version of this article is available at: http://members.shaw.ca/bsanders/WindowsGeneralWeb/RAMVirtualMemoryPageFileEtc.htm
Brief from the article…
Here's a list of how much RAM the various Windows versions and editions support (as of May 2010): Windows NT 4.0: 4 GB Windows 2000 Professional: 4 GB Windows 2000 Standard Server: 4 GB Windows 2000 Advanced Server: 8 GB Windows 2000 Datacenter Server: 32 GB Windows XP Professional: 4 GB Windows Server 2003 Web Edition: 2 GB Windows Server 2003 Standard Edition: 4 GB Windows Server 2003 Enterprise Edition: 32 GB Windows Server 2003 Datacenter Edition: 64 GB Windows Vista: 4 GB Windows Server 2008 Standard: 4 GB Windows Server 2008 Enterprise: 64 GB Windows Server 2008 Datacenter: 64 GB Windows 7: 4 GB
Taken from Microsoft Support Article http://support.microsoft.com/kb/2267427
Are those limits are for 32bit versions? If that is the case how can some server versions of the OS support more then 4 GB?
That is because of PAE (Physical Address Extension)