MegaRAM is the term to designate a cartridge that contains RAM mapped as a MegaROM. MegaRAM are supposed to be write-protected by default. Data is lost when MSX is off.

It allows to execute ROM images exactly as the original cartridge with same ROM mapper, and according to the MegaRAM type and software used, it allows to also execute them exactly as the original cartridge in 80% of cases when ROM mapper is different (using patches).