|One of the biggest advantages of a 64 bit OS is the vastly larger private virtual address space available to applications, but only native 64 bit applications take full advantage. In a 32 bit OS this address space is 2GB by default with a maximum of 3GB. This is completely independent of RAM size. For some large applications this was a serious limitation. For a 32 bit OS this is a hard limit that cannot be exceeded.|
With a 64 bit OS this virtual address space is multiplied by 4000 to 8192 GB for each 64 bit process, again completely independent of RAM size. And this is not a hard limit but one imposed by practical considerations. In future 64 bit systems this could be further increased. This will be a major advantage for large database applications, image and video editing, and games. 32 bit applications will see only a modest increase to 4GB, but only if they explicitly indicate compatibility.
At present there are few native 64 bit applications but that will change when 64 bit systems gain market share. Even now Server 2008 R2 is 64 bit only and Windows 7 may well be the last Microsoft OS available in a 32 bit version.