I've been using my MaBook Pro happily for months but only recently realized that 1 GB is missing. Is there something wrong with my MacBook? It seem to runs fine.
Usually this is because you're using a 32-bit operating system rather than a 64-bit one.
Which MBP? My wife's 3 year old 15" MBP has a published maximum memory of 3Gb. My 1.5 year old 17" MPB has a published maximum memory of 4Gb.