It is surprising that the move to 64 bit operating systems has taken so long. Intel and AMD processors have supported 64 bit operating systems for several years now. If you install 8GB of RAM with Vista 圆4 you get to use 8GB. With the recent operating systems there are options for an application to use 3GB using the 3GB switch in boot.ini.Ħ4 bit operating systems can essentially address an unlimited memory space (at least very huge for practical purposes). When Windows NT was first developed the limit of 2GB per process was arbitrarily set for applications. But I haven't seen any non-server apps use that feature. Some server applications such as database servers use this AWE memory for buffer space. There is a mechanism to use memory above 4GB in a restrictive way. The actual amount used with 4GB of installed RAM is somewhat under 3.5GB. Actually Windows XP 32 bit can't use all 4GB for esoteric reasons. That is why there is the limit for 32 bit operating systems. The biggest number that can be referenced by a 32 bit integer is 4 billion which is the same as 4GB.

Windows xp 2002 service pack 2