MSX 64k games ROM program

MSX supports ROMs up to up to 32k without a mapper mechanism. Larger ones require a mapper as it would otherwise overlap with system memory/bios.

You can definitively use up to 64kb without a mapper. But to access the info in the first 16KB of the ROM the assembler code needs to swap the BIOS out, which is a pain. And to access the last 16KB of the ROM, you need to swap out the RAM, which is an ever bigger pain. That's why most non-mapper ROMs are 32KB, using the middle 32KB. But in principle, you can use all 64KB without a mapper.

In Uridium (commercial version) the last rom page in c000h is used to store code and data that is relocated to ram in 0000h at setup. After the setup the game swaps the rom and the ram at 0000h during execution using slot swap as it waere a two page mapper

On a Z80 register, there is plenty of them

@mjnman

16KB and 32KB ROMs are very easy.

48KB (0000h~BFFFh) can be supported without too much pain if the frame-0 is only used for data. It can be read using the BIOS RDSLT function. You can, i.e., store compressed graphics there.

64KB ROMs are totally nonstandard and not worth the pain. There are a lot of places where things could go wrong and end up only working on a few plain-vanilla machines without any extensions connected.

If you need more than 48KB of ROM, the wise decision is top go for an ASCII16 megaROM. It's a ridiculously simple circuit that will cost you much less time/resources than trying to solve the problems of the 64KB plain ROM approach, with the added bonus that it allows you to go much further than just 64KB.