whether or not a rank of memory in a memory module is busy or ready for another access to alleviate the non deterministic nature of erase and write operations to non volatile memory modules while one or more memory channels 213 a 213 n are upgraded to use non dram type memory modules 214 a 214 n and the associated processor socket 112 b is filled by a non dram memory controller 212 the structure of the mother board 200 is similar to the structure of mother board 100 the prior discussion of elements of the mother board 100 having the same reference numbers on mother board 200 are incorporated here by reference for reasons of brevity fig2 b is a functional block diagram of an upgraded computer system with a dual memory controller 212 u2032 plugged into a processor socket 112 b of the mother board 200 u2032 the dual memory controller 212 u2032 includes a non dram memory controller 212 and a dram memory controller 121 co packaged together to respectively control access to non dram memory dimms 214 a 214 n plugged into sockets 115 a 115 n of the memory channel 213 n and dram memory dimms 114 a 114 n plugged into sockets 115 a 115 n of the memory channel 113 n the dual memory controller 212 u2032 plugs into the processor socket 112 b and couples to sockets 115 a 115 n in the memory channel 213 n by printed circuit board traces 125 a and to sockets 115 a 115 n in the memory channel 113 n by printed circuit board traces 125 n fig2 b.