Understanding DDRn SDRAM
DIMMs have 64 single ended data lines, and they will be divided up among the chips - say, 8 chips with 8 data lines each, or 16 chips with 4 data lines each, or perhaps on a small module you could have 4 chips with 16 data lines each.  Super high density modules may even have 32 chips with 2 data lines each.  Each data line will be connected to only one of the memory chips.  The address, control, and clock lines will be connected in parallel to all of the chips on the module.  Some modules will even have two ranks of chips that are connected in parallel to the data lines, only one of which can be accessed at any given time.