http://www.microsoft.com/windo... The major difference between 32-bit and 64-bit Windows is memory support. Currently, 32-bit Windows is capable of supporting up to 4 GB of system memory, with up to 2 GB of dedicated memory per processor. Windows XP Professional x64 Edition currently supports up to 32 GB of RAM, with the potential to support up to 16 terabytes of virtual memory as hardware capabilities and memory sizes grow. Customers will find Windows XP Professional x64 Edition to be near feature parity with 32-bit Windows.