This book is a summary of the ROM/RAM of the MSX. HRA decided to write this book because there are many different ROM/RAMs in the MSX and he has not seen any material describing them all in one place. This book is aimed to MSX programmers.

For the MSX alone, there is a wide range of memory space switching between basic and expansion slots, mapper segment switching using memory mapper-compatible RAM, and Panasonic-specific megarom bank switching for MSX2+ and later Panasonic machines. In addition to this, the mega-ROMs installed in the cartridge slots (ASCII-8K, ASCII-16K, Konami-8K, Konami-SCC, Konami-SCC-I) and Panamusement cartridges are also described. He has tried to cover all the major ones. Minor items are omitted because they are already difficult to obtain or there is no information to control them.