In another forum, I have an interesting discussion with another MSX user about the Memory Mapper.
He says that since each slot in an MSX2 could contain a Memory Mapper extension, the maximum memory an MSX2 could address through a multiple Memory Mapper configuration would be 4096Kb x 16 slots = 64Mb.
OTOH, I say that the MSX2 norm never defined the Memory Mapper that way, and that since the bank switching can only be made through the reserved $FC, $FD, $FE and $FF ports, it can only address a maximum of 256 x 16Kb = 4096Kb (or 4Mb).
Of course, I can imagine that any hardware solution could overcome that limit, since we could imagine a complex Memory Mapper management, where you could send 2 bytes through the existing ports, therefore increasing the theoritical capacity to 65536 x 16Kb = 1Gb !! Or even more with more bytes, but that would be outside the norm as explained by ASCII in the MSX2 Technical Handbook ...
What do you think ?
PS : Of course, we understand this is nothing but a philosophical discussion, but nonetheless interesting 
