Windows Vista 32-bit version shows less than 4 GB RAM installed when in fact that capacity is actually installed due to 32-bit architecture limitations.
It is not necessary to expect that if you install more than 4 GB RAM in Vista,it will provide better performance because it can’t see more than the above limit by default.If you really need to leverage more,than use the 64-bit Vista versions for better performance.
Anyway,the amount of RAM that can be recognized by 32-bit Vista can be changed by the in-built bcdedit command.BCDEDIT – Boot Configuration Data Store Editor is what was boot.ini in earlier Windows versions.
To change the memory capacity to more than 4 GB,use the following command from command prompt with administrative privileges:
bcdedit /set PAE forceenable
Successful output will show operation completed successfully.
What this command does is enable Physical Address Extension (PAE) within the boot config store to see more RAM present in Vista.
To reverse the command,simply type at command prompt :
bcdedit /deletevalue PAE
For more technical info on this,this Microsoft KB article is the place to be.
Hope this has been an informative post.