PURPOSE: To provide a virtual address assignment method for memory device which improves the operability and the general usefulness and prevents complication of the circuit constitution, the rise of the cost, and the increase of the occurrence rate of malfunction.

CONSTITUTION: On the assumption that SIMM boards are set to slots 1 to 4, data '55AA' or 'AA55' is written in proper positions of DRAMs of slots 1 to 4, and thereafter, data are read out from the same addresses, and discrimination is carried out about setting or non-setting of SIMM boards to slots 1 to 4 and storage capacities of DRAM chips on SIMM boards in accordance with coincidence or noncoincidence between written data and read data, and the overall storage capacity of the whole of the memory is calculated based on the discrimination results, and virtual addresses are assigned to the whole of the memory of the memory device based on these results. Thus, it is unnecessary to preliminarily determine the order of setting of boards to slots 1 to 4 or to discriminate ID signals of set boards.