@Peter, I wish your friend was right, but he is not. Just ask him why modern computers come with beefier RAM amounts while there is a "physical ceiling" imposed by an older Mac book pro, O.k? It would make more economic sense to have a Gb of memory since it keeps machines cheaper if we were to think like him, isn't it?

As @Dennis mentioned, you need to have a processor with more than 32 bits to physically be able to access memories of higher than 3Gb on a computer hence the shift to 64 bit computing to modern machines and faster servers.

Martin.