It's all explained more or less here:
https://wiki.neogeodev.org/index.php?title=NEO-SMA
That's a chip that SNK created, but actually you can create a bank switcher of your own and have so much memory as you want, you just change the bank and have extra 64Mb available for gfx, for example.
https://wiki.neogeodev.org/index.php?title=NEO-SMA
That's a chip that SNK created, but actually you can create a bank switcher of your own and have so much memory as you want, you just change the bank and have extra 64Mb available for gfx, for example.