What do you mean by Rank in DDR3 Design Document?
A memory rank is multiple chips with common address lines. Hence for 64 bit DDR3 bus, we need either 8 DDR3 x8 chip or 4 DDR3 x 16 chips to make a rank.
By the above definition, what happens if we have 2 ranks? the 2 sets of DDR3 will not be addressed by similiar address lines?