GameBoy Programming Manual 13 years ago
The NES had 32K addressable RAM...while some behemoths like Castlevania 3 (http://en.wikipedia.org/wiki/Castlevania_III:_Dracula%27s_Cu...) had 256K of program code to fit in that little box. Every game company solved this problem differently, it seems: http://wiki.nesdev.com/w/index.php/Mapper