The Musical Memory Mapper (MMM) cartridge is a standard memory extension of 1024KB for MSX1, MSX2, MSX2+ and MSX Turbo R.
However, it has other features. A sound chip SN76489AN found in various game consoles of the 80s has been added. The aim is, among others, to run on MSX the console games that have this sound chip as main difference with the MSX. Softwares are provided to run games of the Sega SG-1000 and Colecovision. Thus the sound is identical to the original!
The Musical Memory Mapper also has a write protect function and the ability to manage its memory regardless of other Memory Mapper to make easier to launch MSX ROM images.