Xp x64 not showing 4gb ram

[illuminate]

okay, so i have both XP pro x32 and x64. I decided to switch to x64 so i could max my 4gb of ram. (i'm waiting for windows 7 to get a bit better... chill on the flaming for this decision please).

I have read and been told that x64 bit OS's will accept 4gb+ of ram. while x32 only will accept a max of 3.25.

Why would XP Pro x64 only be recognizing 3.25gb of ram just like Xp Pro x32 does?

 

[Violator]

Some motherboards require you to enable memory mapping in the BIOS before it will recognise all the memory installed.