It is incorrect because 4*8bit doesnt give you enough bits for the 64bit data path.
The 16x (256Mbx16Bit) could work if the memories are capable of paralleling their outputs together, because you would need 4 sets of 4 chips with their outputs in parallel and one of those four would be active at a time, which gives you 64 bits on output and a choice of four different memory sets.

So 4x(1024MBx16) is correct then?
4*1024=4096 and 4*16=64.

 

yes that is correct

 

Thank you very much.. That's all what I needed.

Can you just confirm if it's correct in a case when memory is 8GB?
org= 8x(1024MB x 8) and
org= 4x(512MB x 16) ?