FSX recognizing RAM

How do I get fsx to recognize all my ram? I've got 4gb of RAM, however only 50%, making it 2gb is used.
Flight Simulator and other chat
https://forums.simviation.com/phpBB3/
https://forums.simviation.com/phpBB3/viewtopic.php?f=21&t=64648
Do you have SP2? If so, FSX should already recognize more than 2 gigs.
What's your OS? (32 or 64 bit?).
If it's 32 bit, you'll need to do something special (check Nick's optimizations topics for more info), to make the OS recognize more than two, and even then, you can only use something like 3,4 or 3,7 gigs.