32 bit XP kan maks klare 3 Gb:
http://www.microsoft.com/whdc/system/platform/server/PAE/PAEmem.mspxWindows XP Professional and Windows Server 2003 Memory Support. The maximum amount of memory that can be supported on Windows XP Professional and Windows Server 2003 is also 4 GB. However, Windows Server 2003, Enterprise Edition supports 32 GB of physical RAM and Windows Server 2003, Datacenter Edition supports 64 GB of physical RAM using the PAE feature.
The virtual address space of processes and applications is still limited to 2 GB unless the /3GB switch is used in the Boot.ini file. When the physical RAM in the system exceeds 16 GB and the /3GB switch is used, the operating system will ignore the additional RAM until the /3GB switch is removed. This is because of the increased size of the kernel required to support more Page Table Entries. The assumption is made that the administrator would rather not lose the /3GB functionality silently and automatically; therefore, this requires the administrator to explicitly change this setting.
Du kan tilsyneladende hjælpe på dette med PAE:
http://www.microsoft.com/whdc/system/platform/server/PAE/pae_os.mspx64 BIT XP supportere op til 16Gb:
Benefits of 64-bit Windows
Additional Performance and Scalability
1.
Large memory support. Supports up to 16 GB of RAM
http://www.microsoft.com/technet/prodtechnol/winxppro/evaluate/xp64ovw.mspx