Image Number 17 for United States Patent #6392950.
In order to implement a memory having a large storage capacity and a reduced data retention current, a non-volatile memory, an SRAM, a DRAM, and a control circuit are modularized into one package. The control circuit conducts assignment of addresses to the SRAM and DRAM, and stores data that must be retained over a long period of time in the SRAM. In the DRAM, a plurality of banks are divided into two sets, and mapped to the same address space, and sets are refreshed alternately. A plurality of chips of them are stacked and disposed, and wired by using the BGA and chip-to-chip bonding.