Abstract: A memory system for use in a video game system or the like that has a limited number of signal lines for communicating address signals and a data bus, includes random access memory (RAM) to augment that contained in the game console in addition to plural segments of read only memory (ROM). A first decoding circuit is coupled to the data bus and to the signal lines that communicate address signals to the ROM segments, and in response to detection of a predetermined address and a predetermined status of selected data lines produces a signal that selects one of the plurality of ROM segments of memory locations. A second decoding circuit is coupled to a selected group of the address signal lines, and also to a segment of the memory unit set aside for random access memory (RAM) to which the others of the address signal lines are also coupled.